Cannot answer incoming calls - shows red phone icon with bar across it

Follow these easy instructions to answer a call.

1. Choose one of the following options: Answer call, go to 1a. ...
2. Tap the accept call icon and drag the icon right.
3. Tap the reject call icon and drag the icon left. ...
4. Tap the upper or lower part of the Volume key when you get a call.

https://devicehelp.optus.com.au/samsung/galaxy-s-iii/calls-and-contacts/answering-a-call-on-my-mobile-phone/

View & delete call history You can see a list of calls you've made, answered, or missed. And you can delete calls from that list.
Note: Some of these steps work only on Android 6.0 and up. Learn how to check your Android version.
See your call history

1. Open your device's Phone app .
2. Tap Recents .
3. You'll see one or more of these icons next to each call in your list:
   • Missed calls (incoming) (red)
   • Calls you answered (incoming) (blue)
   • Calls you made (outgoing) (green)

Unable to answer calls - Support forum

https://talk.sonymobile.com/.../Unable-to-answer.../839311

Sony Mobile
11 posts
Solved: Hi, my Z3 compact has been working fine but this evening I suddenly ... Thephone rings out but the swipe icons for answering the call simply don't ...

Unable to answer phone - Android Forums at AndroidCentral.com

forums.androidcentral.com > ... > Verizon Droid Incredible

Oct 24, 2010 - 8 posts - ‎6 authors
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Answering an Incoming Call When you receive a phone call, the incoming call screen opens. If you have previously saved the caller's number in People , the caller's name and number are displayed. If the caller's number is not saved in People , the caller's number is displayed.
Drag to round circle and phone icon to the right to answer the call.
When ending a call, drag the circle with the phone icon to the left to cancel or end a call.
Also attache is a manual, check page 25

https://www.consumercellular.com/Content/PDFs/Manuals/Huawei%20Vision%20Manual%20-%20Final.pdf

Hi,
To cancel bared incoming calls on your phone, enter one of the code given below.
##67#, ##21#,##62# or ##61# then okay/send/yes. the phone will be unbarred.
Regards

The @ represents pressing the "Send" key on your mobile

##002#@ all call diverts off
*#06# IMEI Number showing
**004*DestNo#@ set all conditioned call diverts to DestNo on and active
##004#@ all conditioned call diverts (busy, not reachable, no answer) off
**21*DestNo#@ Automatic divert all calls to DestNo on and active
*21#@ Automatic divert all call DestNo activate
##21#@ Automatic divert all calls to DestNo off and inactive
#21#@ Automatic divert all calls to DestNo deactivate
*#21#@ Automatic divert all calls to DestNo status
**61*DestNo#@ Call divert when not answered on and active
*61#@ Call divert activate
##61#@ Call divert when not answered off and inactive
#61#@ Call divert deactivate
*#61#@ Call divert when not answered status
**62*DestNo#@ Call divert if not reachable on and active
*62#@ Call divert activate
##62#@ Call divert if not reachable off and inactive
#62#@ Call divert deactivate
*#62#@ Call divert if not reachable status
**67*DestNo#@ Call divert when busy on and activate
*67#@ Call divert activate
##67#@ Call divert when busy off and inactive
#67# Call divert deactivate
*#67#@ Call divert when busy status
**03*330*oldPW*newPW*newPW#@ Changing the password for call barring
**33*PW#@ Barring all outgoing calls on (PW one row before)
#33*PW#@ Barring all outgoing calls off
*#33#@ Barring all outgoing calls status
**330*PW#@ Barring all calls on
#330*PW#@ Barring all calls off
*#330*PW#@ Barring all calls status
**331*PW#@ Barring all outgoing international calls on
#331*PW#@ Barring all outgoing international calls off
*#331#@ Barring all outgoing international calls status
**332*PW#@ Barring all outgoing international calls except homecountry on
#332*PW#@ Barring all outgoing international calls except homecountry off
*#332#@ Barring all outgoing international calls except homecountry status
**333*PW#@ Barring all outgoing calls on (PW one row before)
#333*PW#@ Barring all outgoing calls off
*#333#@ Barring all outgoing calls status
**35*PW#@ Barring all incoming calls on
#35*PW#@ Barring all incoming calls off
*#35#@ Barring all incoming calls status
**351*PW#@ Barring all incoming calls if abroad on
#351*PW#@ Barring all incoming calls if abroad off
*#351#@ Barring all incoming calls if abroad status
**353*PW#@ Barring all incoming calls on
#353*PW#@ Barring all incoming calls off
*#353#@ Barring all incoming calls status
*43*#@ Call waiting on
#43##@ Call waiting off
*#43#@ Call waiting status
**61*DestNo**Seconds before divert#@ Divert call if not answered for 'seconds' (Note: Seconds must be 5, 10, 15, 20, 25, 30)
#30#DestNo@ No presentation of the number of the incoming call (CLIP)
*30#DestNo@ Presentation of the number of the incoming call (CLIP)
*#30#@ CLIP status
#31#DestNo@ Your number will not be send for the actual call (CLIR)
*31#DestNo@ Your number will be send for the actual call (CLIR)
*#31#@ CLIR status
*76#@ Presentation of the number under which I reached the other one (not his number if he has turned on a call diversion!) (COLP) on
#76#@ Presentation of the number under which I reached the other one (not his number if he has turned on a call diversion!) (COLP) off
*#76#@ Presentation of the number under which I reached the other one (not his number if he has turned on a call diversion!) (COLP) status
*77#@ Presentation of the number under which the caller has reached me (not my number if I have turned on a call diversion!) (COLR) on
#77#@ Presentation of the number under which the caller has reached me (not my number if I have turned on a call diversion!) (COLR) off
*#77#@ Presentation of the number under which the caller has reached me (not my number if I have turned on a call diversion!) (COLR) status

This means you have no service in the place the phone is at.

You need to go somewhere where you get full service and try it.
power down,remove battery,replace battery, then see what it says when you are in a place that you would get good service.

Still have problem, go to your phone carrier and have them check the sim card and your service, it could be your shut down.

Find here an english user manual for SciPhone i68