Breach of contract

We app**** for a Home Internet wifi for 120GB, but we are getting 100GB instead. We are now in our 4th month with the contract and i have complained about it, but every time i make a follow up i'm being told they will revert to me, but no one bothers to come back to me.

This is definitely a breach of contract, we are being debited the correct monthly installment, but foe the wrong package. I really must say that the service from MTN sucks.

I had requested that they at least refund us the difference for the months that we had paid for in full for less GB