I borrowed #7500 worth of airtime from MTN yesterday and I paid back today but the borrowed airtime is not in my account

I borrowed #7500 worth of airtime from MTN yesterday and I paid back today but the borrowed airtime is not in my account. And while I tried to buy data plan with it yesterday, they were telling me insufficient funds. And now, after paying off the loan, the airtime is not in my account balance. Why is that? I request they send my airtime to my account