MTN Large Unauthorised Debit and NO HELP IN GETTING MONEY BACK

About one month ago my husband got those portable wifi routers from MTN, La Lucia, Durban. It worked fine and we returned it a month later (with receipt as proof). But suddenly, my husbands account was debited of about R4 000 with no explanation as to why such a large amount was debited and why it was debited AFTER we returned the router! We have been dealing with MTN in La Lucia Mall and we have been getting no luck in escalating. They keep telling us that it shows that we returned the router and they will escalate but this promise of escalation has been going on for about one month.

Its disgusting that MTN can just debit such a large amount off someone's account (with no explanation) and make the process of getting the money back so taxing !!