Mtn pathetic Once again!!

On the 8th May I went to a mtn Westgate to take out a mtn data contract, it was 20GB day and 20GB night for R199.99 I was told I would only get pro rata data and on the 12 I would be topped up with all of the above however I was received 5GB. I tried calling numerous times in to get this corrected but no luck. I call the contact centre they advise I need a copy of my contract I didn't receive a copy. I went in to the store which is an inconvenience to see if someone can assist me but they advising me to call the contact centre. You quick to take money but can't help when I need assistance. If this is not corrected I want this contract cancelled as I'm not being charged double and not getting what I paid for!!! I always have a issue with mtn but keep going back. i want my contract and i want the data i paid for.