Voice mail msg

I’ve had “voice mail msg via phone co.” On my landline phones for years  I spent an hr on the phone with customer service who said it was from the answering service we get through Xfinity.  We don’t/haven’t ever used it so we had them take that feature off.  We still were getting the same message and were told to hit #11.   That makes it go away for about 15 minutes.  How do I get rid of it permanently?  It’s so irritating that I just want to throw my phone.