FNB stole my money

I paid my personal loan upfront and the day after they took another payment from me even when the loan was paid in full. They told me told me on the 15th Dec it would be refunded same day. A week later no payment received. then I called again then they told me 5 working days. After 5 working days I called again and they said they raised the issue and can take another 3 working days to get feedback. I don't feel like FNB is even trying to assist me on the mistake they made.