Being forced to pay for Non-service

These big companies need to be reigned in as they are ripping customers off their hard earned cash. Been with this company since 2018 and never missed a payment and saw through my 3 year fixed contract with them. Upon the expiry of my contract they continued to debit me monthly saying the contract is now on a month-to-month since it has matured. 1 bad month for me and I miss a debit order they logged me out of their app whilst continuing to bill me for the service they are not offering. I spoke to them multiple times that I want to cancel but still they failing to cancel my contract with them. They continue to bill me even today 6 months later but I have no valid contract with them neither will they let me cancel. The Ombudsman needs to bail me out here, I will be contact him. These guys are bullies