Problem with refund for phone exchanged

I have talked and chatted with customer service agents 4 or 5 times and even received an email stating that I would receive a $450 refund for a phone I turned in when I bought my Galaxy S-24. The phone I turned in was returned due to a store agent error. I have an email stating "We have credited your account for $450.00. You'll see the amount reflected in your Xfinity Mobile account."  I have not seen that credit. I chatted with an agent 3 weeks ago and 10 days ago and they said I would see the credit in a few days. Still no credit. I do not see any way to Direct Message on my account page. How do I resolve this?