Supersonic - worst service provider

I cancelled my Supersonic Account in Dec 2022 and served my notice period in Jan 23. They charged me for Feb 23 when my account should have been closed. I spend thousands of hours calling them and trying resolve the issue. Their call actually agreed to close the case and credit my account. One year later, they send letter of me owing them for the amount in Feb 23. There service levels are 0/10. The worse internet service provider. I called them on 2 days ago and the manager was supposed to call me but nobody called me.