Unable to cancel contracts

MTN refuses to cancel our contracts despite requests for months, their MTN stores refuse to assist with cancellation of a contract as well. Their customer support is atrocious we have had to resort putting stop orders in at the bank so they can no longer take money from our accounts, cancellations were requested on letterheads per their procedure with copy of the directors ID but they simply refuse to cancel, on the one contract they claim it is already on pay as you go and that the funds have not been taken from our bank but we have the transaction on our bank statements to prove it, absolutely pathetic and unacceptable.