Apple Watch can’t receive calls and shows another number while making calls

I replaced my broken Apple Watch 7 with my old Apple Watch Nike 4 about two weeks before Apple Watch 11 was available. I paired the watch with my phone and had cellular set up. But it didn’t work and Xfinity mobile couldn’t solve the problem. A Xfinity Mobile staff said I needed to buy a new watch. Then I followed his advice and bought an Apple Watch 11 when it was available. But after the new watch was set up, it still can’t receive calls. I can use the watch to make calls, but it shows another number. I tried to call that number and it’s never reachable. It has been more than a month and Xfinity Mobile is still unable to solve the problem and asked me to keep waiting. That is ridiculous. Xfinity mobile’s service is horrible and I’m done with it.