How do I block a number coming in to my mobile Doro 6520

Turned off phone, turned on again, looked for settings(now there), flipped thru contact/message/etc screens, and it now works! Wonky fix, but now works.(I HATE this phone)

Yes off course because you can delete the number on your phone but not on blacklist or block list and make sure the blacklist is ON.

I believe it indicates a loose memory card, but I didn't see it in the manual.

Free manual from the manufacturer's web site:

https://www.doro.co.uk/doro-6520.html

Start by going to “Contacts” and tap on the contact you want to block. Then, press the menu key at the top left of your Doro 6520. You will see a menu where you will select “Block Number” or “Add to Auto Reject List”. The title may vary depending on the model you own

This site seems to address the problem:

http://deviceguides.vodafone.ie/web/doro-6520-proprietary-os/explore-your-phone/internet/set-up-your-phone-for-internet

Follow the instructions on the screen to set up your phone and prepare it for use.

1. Find "Reset all" Press the Navigation key. Select Settings. Select Security. ...
2. Restore factory default settings. Key in the phone lock code (default is 1234) and press the Navigation key. Press the Navigation key to confirm.

Doro 6520 - Restore factory default settings - Device Guides

https://userguide.vodafone.co.nz/doro/6520...os/basic.../restore-factory-default-settings/.
or go to this link might help.
How to reset clock on 6520 mobile Google Search