Telkom Billing Error- I have been billed more

Telkom is very unprofessional. I recently took a phone on contract with telkom (greenstone branch) . I signed up for a 800mb data deal with them only to find out through invoice that they've been billing me Extra, they've been billing me for a 1.5gb data deal.

I brought this to their attention and the ladies at the store ( Thembi and their other has a name that starts with K) told me that because a certain period has lapsed they are unable to undo the error that they've made and I will need to wait 3-6 months to have their error undone. The lady that processed the contract for me has incorrect information for fields within the form itself and the invoices sent to me don't even reflect my adress.

This is very unprofessional and intolerable!! I have to wait while they keep taking extra money from me?! I will not be using telkom services going forward and would not recommend it to anyone.

I need this matter urgently sorted out.