Higher billing than what I signed for

Hi

I recieved a bill which was higher than what I signed at the Vodacom shop. After explaining the issue to 2 call centre agents I finally found a 3rd guy who understood the issue (I did send him an email with my singed document of per month bill that I singed at the Vodacom shop) and told me yes my billing had an issue as I was suppose to recieve two discounts and I only received one. For this he will escalate the issue. I received a reference number and a week later his message -

Thank you for your patience and cooperation. Your query with ref number 1- ********** ********** has been resolved.Billing is correct you received two discounts on the number and it should only be one discount . Thank you, Vodacom

Guess what no explanation how I have received two discounts. No correction of billing - how can you charge something that I did not agree to.

Really bad service