Regretting ever taking this contract. Day light *******

I took out a wifi contract that was on their August catalogue and was supposed to be receiving 50Gb anytime data and 30G night data for R329 per month including mifi router. MTN is giving me only 20G day and 20G.I went back to the shop after realizing that and was told to contact their customer service since they didn't see anything wrong. I left and then communicated with their Service champion who said I should go back to the store as this was captured incorrectly. Went back and told the lady who did the contract is off and will get back to me when she is back. Called her after not getting any feed back and she told me am not the only one with this problem its not her fault it's the system. Really? Is it how you tell a customer that they are not the only ones with a problem after you have taken their money for 2 months and not delivered. Am really angry, disappointed and feel cheated by MTN. Please give me my data or cancel my contract if you can't deliver.