Debicheck Stuff up

I took a month to month Contract out with MTN which FNB put a debit check mandate on. However the installment amount on the month to month differs from the Debi-Check Mandate which resulted that MTN did not get paid. This landed a result now I have to sit without internet for the whole of August . I paid them manually via the QR code on the invoice but now the money is sitting in reserved how long will it take for the money to get to them?

FNB you were always the best but lately your debit orders take too long to process and as a result my creditors complain that they don't receive payment or late payments,

Please advise.