Payment dispute

The worst company to deal with. I had a 18month contract with them. Cancelled my debit order because the arrangement was Eft payments. Paid them every month. Phoned there accounts department in December 2021 to ask what is outstanding. Received a letter to say from there accounts lady to state my account has been settled. Now they hounding for payment insisting I had a 24month contract. No contract sent to me so far. I emailed them the letter stating I'm up to date. I have heard of many complaints from people that I know that dealt with them