Complain against bad service and unfair treatment by Multichoice

I’m very disappointed and irritated with Multichoice,I used to have a decoder in 2010,and I cancel it 2014/2015,in August I bought explorer when I had to make my first payment I was given my old acc of which I told thin that I don’t want to use that as they might end up activating the old decoder I was assured that will never happen,on the 06/10 I noticed that my services were blocked when I call I was told about the money I owe while I made a full payment for the explorer,some reason someone from their side activated the old decoder and they took my payment and split it for what reason I don’t know I have been calling them more than 10 times none of them are unable to help me,one thing that I don’t understand how can a big company like Multichoice don’t have a complaint department,I’m so tired of calling and nothing is done..