Over Payment

In March this year we signed up for the DSTV explorer special for R799 x 24 months. <br> We only received the decoder in May. End of May they deducted R2533.60 incorrectly .After numerous phone calls they agreed to use this as credit for the next few payments. As promised in end of June they didn't deduct anything, end of July they deducted another R700 and end on Aug they deducted R799. As I have a credit with Multichoice no deductions where supposed to take place. I have been sent from pillar to post and this cant be sorted out, why are you still deducting when I have so much credit ( that was your mistake in the first place) and secondly how can you deduct R2533.60 when I only signed a debit order for R799?