Useless network provider

The service is terrible, I upgraded my contact end of May and I am supposed to have received 20GB once off, to this day I have not received it and the call centre keeps on sending me reference number whenever I’m doing a follow up, every time I call because they can never call me, they tell me that my ticket is still open yet the turn around time is 72 hours. Why do I to keep business with MTN. I want to cancel this stupid contract