MTN Contract overcharges and no assistance

I have 2contract with MTN and other 2 cancelled ones 3/4years back. recently my account was over debited and when I contacted MTN they told me one of my old cancelled number was billed on my account. I dont even get my statement the message i get states its sent to my previous work email i also upated 4years back. Whan requesteinga refund no one is will to assist they say they cannot refund and am not at fault as they have kept my old numbers stating its a grace period just in case i decide to reinsatet the contract it won't be a difficult case.