Call Centre Agent doesn't Overdraft Facility

Lately I am being bul**** by calls from the so-called ABSA Call Centre due to my overdraft facility I have with ABSA for my Cheque Account. Apparently my account has been overdrawn, but when I checked there was still a lot of credit in that facility. I've having this facility for more than 4 years and never received a call for using that facility. Has the Overdraft policy changed? If I keep on getting these unnecessary phone calls from these amateurs, I will cancel all my accounts with ABSA.