I've been noticing on my call log for my landline that there are several calls to a 200-100-1103 but when I try to call it myself I get a number does not exist error message
Hello, Gingerluv! Welcome to the Xfinity Forums.
There can be a few different reasons why one would not be able to call a number back. It may be that it is set to decline all incoming calls, or could even be a spoofed number.
To best protect yourself, we recommend not calling back any numbers that you either don't know or don't leave voicemails.
I hope this helps, but please let us know if you have any further questions/concerns.