Collection list remobal

I had a contract with MTN that I couldn't keep up with due to some financial hiccups, and my account was handed over to a third-party debt collector. I managed to settle the debt with the collector in October 2025 and have sent MTN the paid-up letter multiple times, but I'm still showing up on the collection list. MTN's customer service hasn't been helpful - they keep transferring me to the collection department and dropping the call.