Poor service and forcing clients to pay for poor services

I am highly disappointed in the service,had a contract with matrix since 2018 and this was a 36months contract which means this expired in 2021.i then reached out to request for battery replacement and do a test.each time I called they would take me from piller to post and actually never even came to replace battery.i was not happy with this company,after several attempts to get in touch with them I then decided to cancel the contract with them.the process of cancelling was just too tedious still,it took me months to have this officially cancelled as they don’t prioritise clients request.so now after receiving confirmation of cancellation the company is still attempting to debit money from my account and they keep calling claiming that I ow them.i have explained myself over 10 times and the still trying to debit and they are even threatening to hand over my account which they mention it is still active….this is the most frustrating experience as i have cancelled the contract and I was never happy.they are forcing me to stay and I asked for a copy of a contract so i can read because they are behaving like as if it was infinity contract….they are acting as if i had rented out a device from them.