MTN breaking contract and taking half of data.

My Father has a 100gb day and 100gb night data contract for 24 months. Now all of a sudden 5 months after he took out the contract he only recieves 50gb day and 50gb night. Twice now we have complained and twice we received reference numbers with a message saying the issues have been resolved. This is blatantly *****ing as paying R1000 for this is anyways stupid since there are places lile axxes that offer it for R700. He would lile to cancel but everyone just shoves him in a different direction and still no full amount of data. Maybe he should pay half since he only gets half.