Loan settled but my account was debited again a month later

Hi, i requested a settlement on my fnb loan in May 2019, the settlement amount was paid and i assumed all was in order as no instalment was called for on 20 June 2019 however to my surprise an amount of +/-R2400 was debited from my Fnb bank account on 20 July 2019. This is unacceptable as no communication was received from peŕsonal loans notifying me that i still owed them any monies. I'm very upset and obviously did not budget for this which has now placed me in a very difficult position financially. I want this money returned to my bank account immediately.