Incorrect Billing Based On What Was Promised

I upgrade with Vodacom in November to the iPhone X and was offered a deal by the sales consultant. The deal was the iPhone X, R350 airtime and a special 5GB data for 24 months at R1069 pm if I upgraded with them telepathically. Being skeptical of these type of deals i questioned everything i could think of. Is the data at no extra cost and will it be as such for the 24 month duration? "Yes". How much will the monthly be for the entire 24 month? "R1069". Does that include everything? "No, the handset insurance is separate". Only the handset insurance is separate? "Yes" After I concluded that I'd take the deal. While I awaited delivery of the new handset i noticed that the 5GB was activated already, which was fine. After the handset arrived and was turned on I noticed that the 5GB had disappeared and instead I had 20GB of data which i was being charged twice for, which I queried. I was told that it's part of a promotion that people get when upgrading and will be discounted (Amanda 02/01/18). I questioned whether this would affect the 5GB and was told it won't they just can't have two active promotions at the same time and will be rectified the following month. The following month the 5GB re-activated but once again I am being charged twice for it bring the bill for the month to R2139.32, for my number, which is R775.32 more than I'm suppose to pay including insurance. I cannot be calling Vodacom to fix account issues every month because they keep changing the terms of the deal given by adding additional cost they think up.