How do I remove channels ?

you'll more than likely have to do this through your my virgin media account, search the site and follow the prompts...

https://www.manualslib.com/manual/507050/Panasonic-Th-50px75u.html

one way is to re scan your channels from the menu option but choose the manual channel search that way you can choose exacltly the channels you want.

When you say the remote doesn't get the channels I have to assume the channel entry behavior changed. I am not to familiar with this brand but these are the basics for most tv's. If you have not removed the cable input to the tv or unhooked anything before the problem started here are a few thing you could try. Push the menu or setup button on the remote and under the channel or setup option on the tv make sure it is set to Cable and not Air or Antenna. Run the tv through the auto channel search to reprogram the cable channels. This process can take close to 1 hour on some tv's since it has to scan through the digital and analogue tuners. This will allow your tv to add the correct cable channels and remove the unwanted ones. You should be able to enter the channel number or move up and down with the channel buttons on your remote.

Make sure that you have the cable option set correctly before you do the auto search. If this is set to "AIR", you'll only be searching for an analog signal. Hope this helps.

( FOR VIZIO TV MODEL VO47L )
Press menu on the remote,
then go to the icon that says TV,
then press down on the remote to change,
"Tuner Mode" for Cable or Antenna.
"Auto Search" for auto search channels
"Skip Channels" for removing the unwanted channels.

If you need a copy of your manual, go here:
http://www.vizio.com/downloads.aspx

The quick user guide is available here: F32648 F36648

Tuning is automatic on this TV, ensure that auto channel search is on from menu.

Advanced Auto
Channel Search
Auto Cable/Air Switch sets tuner
to cable or “off-air” frequencies
during initial setup. Then system
automatically scans for and locks
active channels into channel
memory.

 you must run "auto program search"/"auto store" again and let the TV find the programs. then put them in order and store. 
If you feel some channels are missing, try to find them manually. The auto store function sometimes skips programmes with less tolerant range, even if they are watchable in a fairly good quality. And search slowly and pay attention and go back if you feel you just skipped something. Good luck and lots of patience!
A new aerial sometimes might mean loss of some channels.

I hope it was helpful

sounds like the tuner section of the main pcb isn't working properly.