NO PAID UP LETTER

I have paid my MTN debt via MBD. They are refusing to give me a PAID UP LETTER, they said I should ask MTN to give me that, MTN has advised that they connot give me that so MBD to give me since I paid through them which makes sense. Guess what I paid in 2023 and they have blacklisted me on a debt I have already paid for over 2 years ago. Guys its hard