Multichoice is misleading with their rewards programme

Multichoice rewards system is a ****, wheel of happiness to be exact, after I won numerous items on their wheel my account went haywire, either I was billed higher or lower and when I asked on their fb page I was told that I got rewards hence my bill was like that, in June I wasn't billed and I was told that I wasn't upgraded when I won the upgrade, for July I was billed less. 747, I usually pay 1171 for 2 accounts, for the month of July they have billed me more than 3k, and their response was that I was billed incorrectly due to a system error of which they credited me more months and have now reversed them leaving me with a bill of 3k, they dnt want to own up to their mistakes and expect me to pay such an exorbitant amount, why should I pay for their errors, I dnt knw where they expect me to get the 3k from