Continuous debit order of inactive cellphone contract

I had a contract with intellicell that expired in May and I was told I needed to contact the call centre to notify them of the termination due expiration of my contract in order for them to stop the debit. I did as instructed and the consultant that assisted indicated that it had been stopped no further debits will go off, however there's a R100 I needed to settle in which I didn't understand what was it for, I agreed and come month end they went into my account and debited an entire R450 which was my monthly subscription for the contract, I decided to wait a few days thinking I will contacted by intellicell to explain the reason for debit but that did not happen. The following month same thing happened and I decided to reverse the funds back into my account. To this day I am still receiving debit order mandates from intellicell of R450 in which I don't know why they still want to collect funds from me, when they confirmed that my contract has been terminated. Very unprofessional and ********** activities