HELP, Xfinity is STEALING 880.95 FROM ME!

I have left several messages here with support and on a couple of old messages, but no one is responding. I am writing again regarding the $ 880.95 that Xfinity owes me. I have tried countless times to get help via phone and chat, but no one seems to be able to help me without putting me through an hour of wasted time when I still get no resolution.

To review: I posted here about 5 months ago about Xfinity Mobile not responding to us regarding an insurance claim. I finally got Dave to answer me here but he could not replace my son's phone because it was a limited-edition model. He offered a $1,000 credit. We would have preferred that xfinity replace the phone, but this was the best he could offer.

We came out of pocket to replace the phone via Samsung. Over the last 5 months, we have experienced continual call drops and dead zones. I couldn't complete a single phone call, I mean, without fail or exception, that did not drop. We tried resetting our service, but with no improvement. Literally HORRIBLE service. And when I finally couldn't take it anymore, I decided to go back to Metro, where I KNOW I get good cell service and customer service. But before I did, I talked to 2 people on chat and one person on the 800 customer "no" service number, who all confirmed I would get a check after the account was closed from the credit on my account. I never got an email.  I copied the conversations and can produce them if necessary.

When I tried the chat again today, I met with such incompetence that it made my head spin. I'm really not even sure the agent understood English. She kept saying I do not owe any money. I told her, "Yes, I KNOW!" We literally went round and round for an hour until I gave up. At this point, I am ready to cancel my internet account too, so I never have to deal with Xfinity again. Can someone please help me get a check for the credit balance of 880.95, as promised? That is a lot of money, and I can't lose that. Especially after having to come out of pocket for the phone that Xfinity insurance couldn't replace.