Double charged

Account *** on the 23rd they tried to debit the amount of R599 without my permission I have signed a contract that payment will be debited last day of each month. On the 31.12.24 they went and debited R599 which is my monthly installment. On the 6th Jan 2025 have received an invoice with the outstanding amount , double charged of R1400 ??? Due to be debited on 31.01.25 I want them to explain why are they charging me double payment? Should I continue with this contract or not?