MBD please help!?

This debt collections agency is honestly ridiculous. They harassed me for payment, during lockdown I made a payment on a online payment portal CREATED BY THEM!! Paying my account. Only to be told my account was no longer with them. I made this payment on the 8th of June and to date I have sent countless emails, waisted so much airtime. Trying to get my money back from them because they are unable to hand it over to the new agency. I have asked to speak to a manager on numerous occasions but I am never able to and they never contact me back to try and assist me. So my money just sits there while I still am charged interest on my account?? Please help