MTN Cancelled contract

I cancelled my MTN contract in March before I left South Africa for the UK and am still being billed and the debit order going off. I have contacted MTN on numerous occasions and we go backwards and forwards and I send them the proof that the contract was cancelled and then NOTHING - I hear NOTHING further until the next debit order goes off! This is the WORST service I have EVER experienced. The costs I am incurring to reverse and try and cancel debit orders each month are starting to rise and this is just not fair!