My data is R7392.04 and cant be explained

I have a data contract with altech auto page, for R229 per month which includes 1 gig data, for the past year I have never been billed more than my contract fee. As for June month something is seriously wrong with my account...it has run up to R7397.04 which is completely impossible as this device is NOT used daily but merely as a back up once I've used up 6 other gigs. I was told my data carries over if not used, but was informed yesterday that data only carries over for 30 days?! And that they can't give a reason why it is so high and want me to log onto Internet to find ou more info but I am obviously to scared to...was also told that is there is also with same problem and has been waiting for 3minths for help...so which means I must pay this ridiculous amount.which is excluding vat or my account will be blocked because I have another contract with them for my cellphone and I will have bad name on my credit profile...this needs to be sorted out ASAP