Mtn sim deactivated and they refuse to refund unused credit

My Mtn simcard was deactivated. I use the sim on the afrihost APN, and since there isn’t MTN billable activity, the network cancelled the sim. When I contacted the call center, I am advised that since the sim is deactivated, they are unable to see if there was any available credit on the sim, and hence can’t refund the credit. And they are unable to offer me any direction on how I can claim the credit.