MTN collections- Poor service!

I am incredibly frustrated by MTN. I have been sent pillar to post regarding an account that was handed over to MBD for collections. The account was paid off in December 2023. In 2024 MTN handed over the account to NIMBLE despite it having been paid off. I have been attempting to call MBD with no success, attempted to call MTN legal who instructed me to call MBD and so forth. I received an email correspondence from MBD stating that I am no longer a client of theirs and should direct any queries to my credit provider. I have called MTN collections numerous times to address the problem and I keep getting different responses from their operators. One says my account shows as paid up on their system and will request a paid up letter of which I should receive within 7-14 days (subsequently gave me a reference number, however the paid up letter never came), one says MTN is unable to give me paid up letter I must speak to MBD(as if I have not tried and explained that MBD says I must contact MTN). No one seems to know what to do and when I try and escalate this to managers, I am told they do not have the numbers for the managers. I am fed up because this is now affecting my credit record!.