Debit order still going through my account for a contract I cancelled and now on prepaid

<p>During June I cancelled my contract and switched to prepaid. I was informed that my last debit order will be the end of July / Beginning of August. This morning I got a SMS from FNB indicating my account was debited with 314.94. When I try to log into Cell C self service to view my historical invoices, it is no longer available. I therefore consider the debit order incorrect. Please repay the money!!!!</p>