billing

hello i have been a customer of Xfinity since 2019. I have went from the bundle internet cable and home security to just internet and since December i have paid over $600 to keep my internet services on. I am on a payment agreement and due to being overcharged and my account not being updated after cancelling the cable in April 2020 I still have the same exact balance of 498.00. I am so dissappointed as a struggling single mother I am to the point to where i am ready to disconnecy my services. I was shut off over 5 times in December after making payments. I returned all my equipment. I am not able to keep paying $300 a month and my past due never changing. My bill is suppsed to be $140 with a 34.96 payment agreement. That alone since December should have brought my past due down. Now after barely 2 weeks of paying $300 i was told i owe another $195 and that i still owe over $400 on past due. I am puzzled as to why this is not going down and how in the world Xfinity can expect $300 on a bill that has a payment plan and is not suppossed to be but $175 total