Absolute nightmare with home security

The nightmare that started when I tried to get a security system installed in March 2022 continues. Techs who showed up w/o equip, disabling my blink cameras, problems with WiFi and faulty equip that had to be replaced, paying for install but had to install parts myself that were mailed to me later, and misinfo about what the security system could do were all just a drop in the bucket. Xfinity billed me in full for equipment I got the first month AND charged an installment plan for the equipment I didn’t get. Thought after the first several hour phone call and credit issued for errors (for may 2022 bill) it was fixed. Month after month, after HOURS on the phone, rude agents and credits issued, I got the next bill and was charged for the nonexistent equip again. Last night a 3 hour tech visit to finally replace the faulty equip. Tonight was the last straw. 2 hour and 59 minute call. First agent said Xfinity was going to overcharge me every month and nothing could be done or else it would trigger a larger charge. I asked for a supervisor. She was the rudest person I’ve ever dealt with at Comcast and that’s saying something. Ultimately she was no help except to credit back the money that Comcast has known they aren’t entitled to since May. She assured me (like I’ve heard monthly) it was absolutely fixed. I asked for verification which she said she couldn’t do.  She admitted she couldn’t actually know it was fixed. I have spent 60 plus hours on the phone and missed several days of work for the multiple botched install appts, having to leave work and drive home to turn off the alarm because it’s malfunctioning but mostly because of this absolute REFUSAL TO LITERALLY STOP CHARGING ME  FOR SMOKE DETECTORS THAT THEIR BILLING SYSTEM AND THE INSTALL CONTRACT FROM THEIR TECHNICIAN PROVES I PAID. I am at my wit’s end. Since Xfinity says they have no process by which they will stop charging me for money I don’t owe, what am I supposed to do?