Bad service level on Contacts

I took out a 2GB internet - 3G contract at Nashua Mobile some years ago. Now the contract I signed for states that once I reach my limit I would be notified of this (T&C section 13 of MTN) as Nashua is only a service provider my contract is at MTN. Should I reach the limit I will go over by R10 (T&C section 14 of MTN, also on MTN website). So around Nov14 Nashua contacts me informing me that my contract will move over to MTN directly they as a service provider will no longer manage my account, AND it is stated that no condition changes. So all goes well then I get an account for May in excess of my contract, then in June goes up to 3x my contracted amount. So I start calling the *** call centre whereby I get told by Daniel no I am wrong MTN does not have such a contract and they will not be able to address. So again I phone and find Corrien who informs me on no she sees my problem and that they will correct and credit, gives me a reference number and states 3-5 days I will be contacted and fixed. 9 days later I phone again to be told by Bongani the reference is there but it will take 21 days to address and that they can not be held liable for going over despite the T&C. POOR