incorrect billing

good day

I'm on DStv price lock I notice Dstv has been charging me more, I enquired yesterday I called the girl I spoke to said my last payment was in May whereby I pay every month, now I called they telling me its R1200 I need to pay and they don't know why I'm charged that while I'm on price lock, this woman said she will enquire with billing department and they will call me same day , I'm supposed to pay R549 and R35 of insurance which makes R584 which is the amount I pay now what I see on my account is not accurate and I even have credit on my account , this thing is delaying my august payment I ain't paying this account until this problem is resolved if its not being resolved I want to cancel then. the reference number ***-C1 I spoke to Variksha