bad service

We bought a car from Mazda on the 4th of January, we were told that we have to wait for the funds to clear and for the car to be taken for a roadworthy test. We went to collect it from Mazda on the 11th of January, few days later we notice that the car tyres are old and not in good condition. We then advised the sales person that sold us the car that we are not happy with the tyres can something be done, he kept saying the car went for a roadworthy test and that there is no way the car could have passed. The car was bought cash with no hustles. we are not happy with the quality of the tyres especially the ones at the back. PLEASE ASSIST!!!!!