Complaint FNB

I have been struggling to get my overdraft rebate out of FNB since March 2018 as their system is not equipped to automatically calculate the rebate if there is a payment plan in place. I have to now manually "apply" for my rebate monthly. I have logged numerous calls via phone, email and their chat group and have spent hours on the phone to them just to end up with no one ever getting back to me. Every time I have to explain my whole story to a new call centre agent whom just logs new calls every time saying it takes 7-10 working days with no reply. I don't know what to do anymore. I have been with them for years and have never received such bad service from them.