MTN SIM Deal

Last year September I took a sim deal with MTN and I regret taking it. I honestly have been receiving quite a bad experience. I regret taking it, if there is an option of signing out the contract. When it's due for debit the will not debit instead the will say the debit didn't go through while I have funds in my account. I feel they do do this so I can pay more instead of the the agreed upon amount. I have called the call centre a million times to remind them debit but still they will send me threatening text to tell me that they will hand me over to the lawyer and this is honestly draining. Can MTN cancel my contract, its been four months of stress.