MTN bad service( Store, Call Centre, social network)

I app**** for a 50GB data contact in November 2017 (black Friday weekend) which was approved in January 2018 after following up with store and calling call centre for almost 3 times a day. As if this was not enough, they are now crediting my contract with 30 GB monthly which is 20GB short from what I signed for and what I am paying for. This is a breach of contract and acting in bad faith by MTN. All I get from the store and the call centre is that we are working on the matter. I wonder how long they need to resolve this quiry. If they don't resolve this sooner I will block any debit order they put through. We are getting to February (3rd month) now. This is unacceptable ☹