Vodacom not keeping tonthe contract

I have been talking to Vodacom now for about 3 weeks regarding a problem I have on 2 of my contracts. I upgraded the 2 contracts to 2 Gigabytes each per month in July. Since July I've only been getting 600 megabytes on each phone while paying for 2 gig. This was confirmed as a mistake by Vodacom and I was promised that it would be sorted out. It is now 3 weeks and a couple of phone calls to their costomer service center later and it is still not sorted out. I want the 10 gigabytes that I paid for on each phone to be allocated to the relevant numbers or those contracts cancelled with immediate effect because they did not hold up their part of the contract.