Refuse to pay back money I paid to repair aircon

I bought a lovely car through Avis on 4 December 2015. From day one the aircon was not really working and as a women I don't know much about cars. When my friend arrived at my place I asked him about my aircon and he told me the aircon is definitely faulty as it is not making the car even cold. As the placed are closed and I can't drive around in this heat with no aircon I went to an aircon place where they test the aircon and find out there is NO gas in the aircon and the filter is broken and very very very dirty. Normally when a car is sold I thought they service everyting and that the aircon is included. Well I filled up the Gas and replace the filter which cost me R550, when I sent my complain to Avis with the receipt I received a email back that they won't give me any money back as I have to contact them first before I replace or repair something. I'm dissappointed in Avis and put this email on hello peter to let people know buying from Avis make sure everthing is working and if you are a women don't know about cars, take the vehicle to AA or a place that can test everything, when the finances is done, Avis is not so helpfull anymore. So please be aware!!