Premium collection complaint Account ***7

I had a contract Acc no ***7 with Mix Telematics. This contract ended in January 2023. Their premium collection is in advance meaning January for February. Endless contact made via telephone and email without any success. I have been debited for February, March and now on 25th March debited for April. They have confirmed via email that my contracy is cancelled but they continue to debit my account. I can't stop the payments because they use the debit check system. I need help because they do not respond to emails and I have sent another one on the 3rd March which has just been ignored instead debited my account again.