Overcharged

on August I just entered with the dstv contract price lock to pay R599 for 24 months but just to surprised with the debit of R730 on September and October its saying R640 and I've been calling them since last month and they say I've got 2 decoder on contract which they cant even trace how I entered on the other contract. every time when I call was told the matter is escalated but when I do follow up the is no record of escalated matters and also no feed back. I've last called them last week from Monday to Friday but with the same respond of saying the matter is escalated. am really don't know what to do as this is not the same time Dstv giving me a contract that I was not aware of and overcharged.