Telkom Double Debit

I was hoping you could help. My debit for this month didnt go through as I had insufficient funds on which I take responsibility. I've recently acquired funds, and now the debit has gone off, but it deducted double the amount it was supposed to... Instead of R511, R1029 was deducted. This has now put me in arrears. This is unacceptable.

Failed FNB debit - TELKOMMOBI ********** ********** 027272

Double FNB debit - TELKOM TELK ********** 27V180615