Please close my Account, I settled 3 years ago

I settled my MTN Account 3 years ago. I send them proof of settlement. But they have been handing over my account to different attorneys with status of arrears of accounts.

Why are you so cruel MTN to ruin my credit profile? Even now the account is still running my profile from 3 years of settlement.

Is it impossible to close an account? I'm so disappointed and I will never use you as service