Six year old contract

I closed My account six years back to migrate to Vodacom after my contract ended. A month ago I saw a good deal at MTN and thought I should apply. To my disappointment I was told that I have an outstanding account and I'm blacklisted. I was advised to call MTN. After I called, they told me the account shows it was paid off and the contract was stopped, but it never reached legal department. Three weeks later, the problem is not solved and they keep telling me the legal department is still busy with it. The worst part about this story is, I was never even notified about owing anything. Or even try to resolve the matter while it was early. For such a big company, you're a disappointment. I'm glad my application was denied so that I don't have to deal with you.