Overcharging on price lock account

In July signed up for the pricelock package which is supposed to be R899 pm. Added a 3rd decoder for R95 which brings the total to R994 which is what if my calculations are correct is what I'm supposed to be paying on a monthly basis. Not so. For the past 2 months I've been paying over R1000 for this service. R1630.51 & now I must pay R1260.58. I also cancelled the debit order right after the first payment was made & I advised them I will be paying it cash on the first of every month as per the initial debit order. Now I see the outstanding amount which says it was due on the 24 August of which NOBODY bothered to inform me about. So I'd like for someone to get back to me to explain what has happened and why it has happend and to make sure it does not happen in future.