No limit on data usage set as per verbal agreement

I signed up for a contract on a tablet (nr.***) with Altech Autopage Cellular Mahikeng on behalf of my<br> teenage son, witch he has to pay for from his monthly allowance. Prior to signing the contract I specifically told the manager (Kobus) that it was for my teenage son and that a limit must be set on usage for 500Mb/month and he agreed to that.<br> After 2 months of using the tablet I got the first invoice stating that I owed the amount of R 16000-00. I immediately went to see Kobus and he told me that he could see that no usage limit was set as was agreed initially. I then asked him to rectify the problem with his head office because I was lead to believe that a limit on usage was set as he was asked to do when entering into the agreement initially.<br> Since 1 July 2014, after several sms's and even visits to his shop in Mahikeng by me, I have not received any feedback by means of a sms or a call from him.<br> I have 2 existing cellular contracts with Altech Autopage Cellular (nr.*** and nr.***) for my two teenage sons but both sevices were suspended as from July 2014 due to the outstanding amount on the tablet contract, even though I make regular monthly payments.<br>