Not Delivered on Deal

I purchased the Black Friday 30GB for R199 deal from MTN last year and not once was this delivered to me. Every month R199 is deducted from my account, but I only receive 20 GB. This has been a very frustrating experience. I have been in contact with stores and with customer service and my query has still not been resolved. This has been a very disappointing experience because I left the Vodacom network that was very efficient and always delivered. I regret joining MTN for this suppose "Great Deal", because of the poor service delivery that I am getting. I have thus lost out on 30 GB and surely cannot be expected to complain every month and still not receive what I am paying for!