Overcharged on Overdraft interest

I have an account with Nedbank which i took many years ago with an overdraft allowance of R7800.00

When i took the account, my interest rate for the overdraft was prime interest rate or so i was told

Yesterday when i went through the app, i realized that they have instead been charging me an interest rate of 14.25%

I have already made an arrangement to pay this off and actually close Nedbank account since i suspected that they were overcharging me and now i have proof.

I was all the money that you have been charging me over the years, you guys are undermining our loyalty

I want all my money, i'm really tired of being drained like this. I'm a loyal customer with many other services with Nedbank and now you treat me like this?