Worst service ever

I cancelled my contract with Vodacom in April and have been debited, refunded and then debited again for about 5 months now. Its a pesky R31 being debited but it is beginning to add up. I've spoken to probably 15 agents and 3 or 4 team leaders about this but to no avail. The money is supposedly being debited for 250mb I got on promotion along with a free tablet i got with my phone. I have paid up my contract before the 2 year period and cancelled it, thus ridding myself of all debit orders as confirmed multiple times on my first few calls. I am now fed up and almost helpless and would not recommend this network to my worst enemy. Please help!!!!