Not a working number

This is now the fourth time I've had cell phone issues. Someone calls me and they get the "This is not a working number" message. My bill is paid in full. I've called three previous times and each time they said it is fixed, but it isn't. The only way I know my phone isn't working is when a family member calls me on my landline to inform me of the issue.

This all started when my spouse died a month ago. The account was in his name and I had it transferred to my name. Ever since then I have had issues and the cell phone now gives out "this is not a working number" message. At this point, I am about to switch to Verizon and give up on AT&T despite being with this company for over 15 years. It's just not worth it anymore.