Disappointed 😞

I am more than disappointed with MTN just found out after trying to take up credit that I am owing them and it's been years of which that's not true I have statements to prove that even called in on the last month to make sure and everything was sorted I don't owe them a cent but to my surprise they have been messing up my credit record by reporting false information can you imagine the frustration after being their customer for more than 20 years. I would understand if they saw they made a mistake and removed this debt but they kept it going on for more than 4 years. How does one come back from this? MTN I wish to express my anger so you can fix this mess but can you if u have failed so dismally.