Getting double-billed for mobile line added by mistake

I've had this problem with Xfinity since I moved to a new apartment in September 2024. It took a few tries to get service transferred, and each time I used the in-app chat feature to get it fixed, they kept adding accounts to my profile. I didn't know it at the time, but they added a total of four accounts, two with internet service. I got the internet thing figure out, but the multiple account issue became a curse when I tried to get a bundle deal where I add a mobile line and get a cheap/free phone. I received the phone, but it eventually ended up with two numbers on it at one time because the chat agents added mobile service to one of the other accounts on my profile, so they ended up not giving me the free phone deal. So the account that first received the phone has an outstanding balance of about $250 now. It also has some balance for months of phone service that was never used and was cancelled right away.

I've spent hours in the in-app chat trying to get this resolved. I've spoken to many agents on the phone about this, and each one of them agrees the bill is a mistake. They all added credits to bring the balance down, and I was promised many times that the charges would be removed. However, the bill remained and attempts to auto-pay it occurred every month. I am now no longer using any Xfinity service, so the customer service agents are even more helpless and now hostile because they say this bill is in collection.

I need this bill resolved. I didn't cause this mistake, and I can't fix it on my own. So far, no one has been able to resolve this. Please, I have been trying to get this fixed for almost six months now.