It sounds like you resolved an issue with incoming calls by changing the CSC (Customer Service Code) to VTR. Changing the CSC can often help resolve network-related issues on your phone, as it is linked to the regional and carrier settings.
For anyone else experiencing similar issues with their phone service, here are some general steps that can be tried:
Thanks for sharing your solution!
If anyone else is reading this thread, probably your solution will work for them as well.