Overcharged for the past 5 months

Dont ever get upgrade or get a contract using their online systems. For the past 5 months i have never paid anything close to what my initial installment should be which is R289, last month it was R881 The previous month R400 and the so on. Called them yesterday to find out what my current balance is as of yesterday i was told R480 due to insurance and all, i accepted, this morning i woke up to a R578 debit order.

Been holding the like ever since with no assistance. If its not MTN chowing airtime, they are charging people more than what they bargained for and they dont care in resolving queries, its business as usual for them. Just look at the amount of bad ratings