Mtn service providers are not good to deal with

I had an mtn account 2017 and they were inconsistent i stop paying that account they handed me over to vericred collection services where they collected funds from me to settle the account i did that and paid it in full..but mtn did nothing with that i still have that account as overdue in my credit ..i then called mtn agents they all failed to help me required proof of payment from vericred i obtained it and sent to them into their email address then promised me that after 21days they will remove me from the service and update my credit but they did do that instead they handed me over to Nimblegroup now which keeps on calling me an i am tell them i paid the account in full and even sent them proof of payment but nothing is done.hellopeter please help mtn is a huge problem