MTN over charging me every month

I have been going to MTN in Greenstone mall for 2 months now I upgraded to a Samsung J5 Prime from a Huaiwe P8 Lite in February on the 4th 2018 but since I have upgraded I have had nothing but stress from MTN. On the 20th February 2018 I paid R340 then a few days after I was told I owe R296 I have never not paid a month on my MTN contract I went to query that amount at MTN Greenstone I was told a query would be logged I received an sms days after that's it's resolved, days later again I received the same message a few days later I went back to MTN GREENSTONE and a query was logged again but this time it seemed to be resolved. On the 20th March i went to pay i am thinking my payment should be R287 as I was told I should pay R365 as mg insurance is R149 and other charges I don't understand I paid R290 on the 20/03 I logged a query with MTN Greenstone again so now being the 30/03 I just got a message that I should pay R367 by the 03/04 I am tired of the same thing with MTN I was told by the consultant at MTN that my insurance is R87 now its R149 plus VAT R170 i requested for a copy of the contact im still waiting. I feel so frustrated with MTN