xfinity store incorrect billing

Visited an Xfinity store 4/14/25 to move our mobile service to Xfinity. While there, I accepted offer of a 'free' new iPhone & agreed to purchase an iphone 16+ for a $500 credit with remainder ($500) of the phone’s approximately $1K cost to be billed monthly over 24 months.Employee quoted that to be approximately $21/mo. The employee (without my request or agreement) then proceeded to transfer data from my iphone 12 to the new phone, a process that lasted 2 hours partially due incompetence. She then wiped my old iphone 12 clean so I could leave it at the store, another requirement of the offer. I was told the receipts for the new iphone 16+ and monthly payment agreement would be emailed to me so I left. The next day I received a call from the store employee (NOTE: this is after 4 hours spent in the store and after I updated many individual settings myself) that a "glitch in the system" (NOTE: they input the information incorrectly and failed to credit me $500 for return of the old phone that was left at the store) required me to return to the store and start all over with a "new phone" because they didn't know how to correct their billing error. This error was reflected in my post-visit emailed receipts that showed no credit with erroneous monthly pay-off of $42. Interestingly, I also received an Xfinity email on 4/14 stating "Your Xfinity Mobile Trade-In Case Has Been Resolved", an acknowledgement that Xfinity knows there was a issue before I did the following day. I informed them I would not be able to return due to travel and availability. My new phone is fully set-up and works perfectly. I have already invested the time required by me; this is exclusively an Xfinity-created error, & it is not my responsibility to fix your billing error as I do not work for Xfinity. The manager listened in without my knowledge or permission to 2 conversations I had with the employee over 2 days, and became abusive, refusing to resolve their error and telling me the over-billing was now my problem. Calls to Xfinity's customer service have been wholly ineffective. 1) a 1.45 hour call on 4/15 (Ahmed) led to ticket #ECM13237796 and an unfulfilled promise that I would hear from Xfinity in 2-3 days 2) 4/21 another call, when I and insisted on escalation, eventually led to supervisor ‘Mike’ promising to get back to me (after 40 minutes with him.) His assurance also went unfulfilled. What is my next step? Small claims court? Unless I am informed in writing from Xfinity that the billing error has been corrected I will be forced to consider the entire episode as fraudulence by Xfinity. The level of incompetency & utter lack of accountability shown in Xfinity’s failure to resolve their self-created billing error is astounding. I reasonably require a satisfactory response and a full credit for the returned phone within 48 hours. Thank you.