Angry customer from poor FNB bank service.

I have an issue with FNB loans. I had a loan with them and my last payment was in November as per the email they sent to me. Only to find that they debited twice now in November. When I querried with them they said they re still investigating, what there to investigate cause the double debit is showing on their records. This is so unproffesional and I am so ****ed cause I paid very well for the past 5 years, never gave them any problem. I am now told that my loan ends in December whereas I have proof from the email sent to me by FNB saying my last payment is November.