No resolution on incorrectly billed account

I have 2 MTN contracts that ended in May and when we cancelled these contracts we had 1 more billing cycle left for airtime already loaded. This amount went off in June, however in July a second amount was taken from our account. We queried the issue and we were informed that this was taken in error and the issue was logged for a refund. Since 5 Aug we have called over 10 times to follow-up and spoken to multiple consultants. Each time we are told that the issue is being escalated for immediate resolution but nothing happens. Please could someone assist to get our refund processed. The call centre claims to escalate the issue but there is no progress being made.