Telkom cheating me out of 20GB/month as per their contract

I have a 80GB contract with Telkom Mobile and have recently noticed that I am being charged for data that they are not provisioning. The contract is 40GB anytime data + 40GB night-surfer data, broken down into chunks of 4 x 20GBs. For the last three months (potentially 4 months) telkom has only been provisioning the normal 2 x 20GB anytime data, but only 1 x 20GB night-surfer data - without an explaination. When I eventually reached out to them they flat denied this and promised to email confirmation that all data has been provisioned, which they have failed to do until now, although I have screen prints of a data usage dashboard that proves otherwise. This is a c;lear breach of contract from Telkom and they refuse to reimburse my data or my money, which has resulted in me using more money to buy data to meet my family's monthly data usage needs.