No service at Thrifty O R Tambo

I rented a car from Thrifty (O R Tambo branch) for a certain period of time. After that did I extend the rental period several times.My complaint is that getting hold of this branch on the phone is physically impossible. I have two numbers that I got from the initial documentation and a third number that the Thrifty National Callcenter gave me. All three numbers just ring and ring. This has been my experience for a number of weeks. You cannot get hold of them