I need someone from xfinity mobile to help with a huge problem, going on 8 months of reaching out with no response or help from xfinity

Backstory: April 2022, I left my phone service provider of over 20 years to switch to xfinity mobile. They had a deal going where I would get a free iPhone 12 mini if I kept my number, so of course I accepted the deal. From the moment the phone arrived and I set it up, I had awful reception to the point I couldn’t make phone calls out and the calls would drop instantly if somebody called me. Even my texts barely went through. I reached out after a week of this happening and was promised my problem would be fixed if they sent me a new SIM card. I received the sim, did all the steps I was told to, and nothing changed. I still couldn’t use the phone at my residence and it barely worked anywhere else. Over the next 8 months I reached out continuously to xfinity mobile customer service through chat, and on different family members’ phones to get help with my issue. All they did was run the same diagnostic tests and give me the run around every single time. Nobody was listening to me. So after 8 whole months of paying my xfinity mobile bill for a phone that never worked, I terminated the line. They made it clear to me over the hundreds of times I reached out that they weren’t interested in solving my problem. So now I just got a letter from collections stating I owe xfinity mobile over $450 since I terminated the line and need to pay for the remaining device balance. My question is this, why should I have to pay for a device that never worked in the first place? If xfinity would have gotten the phone to work and helped me, I never would have had to terminate the line. But I was ignored and not listened to for months. Why would I continue to pay for a phone line that I can’t even use just so that the rest of my 24 month bill credits cover the cost of the iPhone 12 mini. That is beyond unfair, and for all of the stress and confusion and upset I went through, I don’t think I should have to pay it. Please put me into contact with someone who can actually listen to my problem and empathize as if they were in the same position. I have never dealt with such awful customer service in my life.