feeling helpless

I was supposed to receive money back from avis as I had hired and returned a car to them. I received a sms from fnb that the money should reflect in my account but it didn't. I called the call centre to an advisor that hung up on me and didn't bother calling back. I called again to an advisor that tried helping me by doing calculations but also hung up on me when they were supposed to assist.I just want to know whats happening with my account and get some assistance.This is a lot of money we are talking about.