Blatantly steeling from customers

I upgraded my contract in May of this year. I noticed that I had a much bigger debit going off after my upgrade and upon investigating found that I was still being billed for my previous handset. I contacted Vodacom and was informed that this is because I upgraded before my previous contract term had ended but got assured that the last , extra handset debit, would go off end of August. Today I find that they have once again debited me the extra amount and once again after investigating I find that there is still another debit scheduled for end of October, still for my old handset. This is blatant steeling from me Vodacom!!! How do you keep charging for something that is already paid off??? The funny thing is, even with you taking extra money from me, had I missed a payment, you would be over me like white on rice!!!