CHARGED R240 FOR PAYING INSTALLMENT EARLY

@TelkomZA I'm shocked! I paid R599 at a pnp store on the 27th of August cause I knew that I won't have that amount in my bank account on the 31st. Hai today (04 September) I'm told I should pay R240 for the bounced debit order regardless that I paid my monthly 5 days in advance Yhoooo Yhoooo why? Day light ******* and I'm having such a rough month I made sure I cover all my bills so that I'm not behind on anything now this?????