I had a data contract with MTN that I couldn’t pay, and the account was handed over to VVM debt collectors

I had a data contract with MTN that I couldn’t pay, and the account was handed over to VVM debt collectors. I arranged to pay the R2,168 owed in 4 monthly debit orders of R542 starting March. Payments were made in March, May, June, and July (final instalment). I requested a payment letter from VVM, but they said since it was a post-paid account, only MTN could issue it. I sent proof of payments to MTN in 2023 via email but got no response. I also tried calling but received no help and gave up. Now, 2 years later, Nimble Group is contacting me claiming I still owe MTN. I shared my proof of payment, but they insist on a letter from VVM, which I can’t get. I’m frustrated because I paid off this account, yet I’m still being pursued for it. MTN or VVM clearly failed to update their records, and this could wrongly affect my credit profile. MTN has handled this very unprofessionally.