Mtn breach of contract

I signed a 24 month contract with mtn, they did not cancel the contract after the 24 month contract expired. I was informed that there will be another debit order month end, which is breach of contract. MTN care line said that I have to call in to cancel my contract, which was never explained to me when getting my contract, I am very unhappy and I can understand why everyone is migrating to vodacom and cell c. I will take legal action against them if this problem is not solved asp, I will not pay another debit order.