Overbilling for more than 3 months

Iv app**** for a pricelock meanig im gonna be paying a certain amount for the next 24months. But to my suprise im billed more than the agreed amount over and over. Iv called the their contact centre numerous times and its not been fixed, i honestly dont know what to do anymore. As we speak im to be billed double tomorrow of the agreed amount and ive been trying to fix this matter the whole week last week, last spoke to UNATHI who put me on hold for more than 35minute without returning till i cut the call and the previous consultants said its escalated and will be fixed but nothing.... what exactly does one have to do to sort this out or should I just deactivate my account? Dstv has become my nightmare with *********** people who never know whats happening or why im being billed more?????