DSTV multichoice

I had 2 decoders....i cancelled tge cheaper one last year . Now and again they charge for both decoders i phone and they promise to rectify the problem, in july they charged me 700 of which previous months i paid less i phoned them to complain they promised to look into it until now no feed back and last month they charged me the correct amount. Please stop ripping me off and many others. Have mercy hayi booo