Bad service from Multichoice DSTV - Being overcharged

I have two decoder on my account and one of them has been inactive for about a year. In December Multichoice decide to active it. I called them to query this and ask for a refund and reversal but no one in their call centre is helping. They keep on saying they get their team leader to call me but nothing. This is very bad service. I'm not willing to pay for something I'm not using. That why they loosing viewers