Double debit - Car finance

Firstly i don't bank with Nedbank but my car finance is with them. September was the 1st month it went off. During the month i got multiple calls from them asking me to switch banks which i declined. So the 1st time i get debited these people double debit me. The first ones goes off the 2nd ones gets rd cause i only keep enough money for the debits. Now the giving me a bad credit score because of this. I would never bank with NEDBANK cause you firstly bombard new clients with calls and now this.