Add on bundle (Billing)

I app**** for the Go 10G contract last year around May....I have been paying R139 for the subscription and in the middle of the month calling the call center to add 10g for R99..which I understand that I will be charged for it at the following month....but now to my surprise I’m now being billed R250 for subscription.....the call center said that it’s because of an add on bundle that I have never agreed to.......Please sort this out I can’t be paying R500 for a R140 contract