Debit order not debited even though there's money in the account.

I have a contract with MTN, they run the debit order on the 25th of every month, today is the 26th , there's money in the account, they haven't debited, I called them, the first guy I spoke with didn't even bother to escalate my query to the relevant department, he kept telling me that he will wait until tomorrow to see if the funds will clear, how can the funds clear when they were not debited? I called again spoke to a lady, said she will escalate to the billing department,the money is still not debited, is this how MTN makes money by not debiting our accounts so that we can fall in to arrears and they charge us arrears interest and tannish our names and our credit profile?