Waiting more than hour for a BOOKED Rental Vehicle

Reservation ***8ZA0. Discovery Health booked the rental car for me on 06/01/2016. When I was called to confirm, I pertinently informed Avis Car Rental, they must please be at DentTech at 12:00 as I need to get back to work. I received notification and assurance the vehicle will be at DentTech by 11:30. Avis called me today at 10:51 to confirm the address where they must send vehicle to, I confirmed the address with them. Today it only arrived at 12:30. The receptionist at DentTech tried non-stop for more than 30min to get hold of Avis as nobody answered the phone. Eventually the phone was answered by Thembi/Thandi who immediately went into attack mode and told me, I called them to advise I will be collecting the vehicle from them... I denied this and insisted on speaking to her manager. I was told she's not there she is in Sandton and will be contacting me back... well it is now 15:05 and I am still waiting for the promised call from her manager... I will think twice before using Avis ever again. The encounter I had with their call centre staff was all but pleasant.