Trouble with returned phone

I had signed up a new line with an iPhone 17 Pro. After receiving the phone, I decided to return it. I got the shipping label, wiped the device, and returned it with all the original packaging and in perfect condition. The phone was received (and acknowledged) by Xfinity Mobile. Some weeks later, I was sent a cryptic email saying the phone was being returned to me. I contacted customer service through chat, told them that the phone was returned in perfect condition. They advised me to send it back to them after I received it. But it never was sent back to me. No information about a shipment was ever sent to me. But in the meantime, I was charged full price for the phone.

I've since chatted with customer service a couple times. A case was opened (ticket ID [Edited: "Personal Information"] but I never heard back. I then got on another chat about this on November 10th. They looked into it and said that I should have a refund in 24-48 hours. That still hasn't happened. 

How do I get this resolved? The agents I've chatted with have seemed to be helpful and working to resolve my case, but I still have the charge on my credit card.