PAYJUSTNOW unjust interest in a single day

Payjustnow was supposed to deduct R186.20 on 22nd January, however such deduction was not successful as the account had no funds. After realising that deduction was not successful I transferred fund to that account and it reflected on 23th January. When I tried paying on the 23 January they had added penalty of R125 making installment R311.20 a penalty of 67%. This is unfair business practice to add such amount for a single day missed payment.