MTN Mobile Money number change

I have been contacting MTN Mobile Money for almost 3 months now because I need to change my number on the Mobile Money account. I've been explaining to them everything via email because you can't get hold of an agent if you tray to call them. I don't have access to the old number, I don't know my last mobile money account balance, when I try to change my number on the app I get the relink was unsuccessful message. 3 months they are failing to assist me.