Nedbank sitting with my credit

Good day. I paid off my loan with Nedbank in 2019. I overpaid by R6400 and have not received this credit back. I was told to wait 48 hours but this time has passed and nobody can help. I keep getting told to phone a different department. How is it ethical that Nedbank did not transfer this credit in 2019 already? They closed the account November 2020 and even then did not notify me or transfer credit. I bank with Nedbank so this should not be rocket science.