MTN contracts / accounts

My contract expired end April. Received a SMS telling me I am on prepaid which I requested in March as per their instruction.. But still MTN deduct my account with a debit order. They deducted end April and now end May. They must be the most useless network that I have had the unfortunate displeasure of dealing with. I must now go back into the bank to reverse the debit order especially the cost of petrol etc.