MTN OVERCHARGING ON MY CONTRACT!

I renewed my contract in October 2018 to a way cheaper contract and I haven't seen a single mention of the new amount on my statement since the start of the new contract. upon calling the call centre I was first told that the discounts that were supposed to be effected on my contract were not loaded and I must allow a 48 hour window for that to reflect on my account. I waited and only saw a portion of the amount taken off but still no major difference on my balance. I called again at the begging of January only to be told that the amounts that I am seeing on my account is due to arrears going back to April 2018, mhhh - how is that even possible? How can you renew a contract when there are still outstanding amounts on the old account? How come I was never locked off my phone if I was such a bad payer? Something is definitely wrong here - MTN can you please rectify this or maybe completely cancel my contract and I can take my business elsewhere...