Tiger Wheel and Tyre
Problem with Yokohama tyres and passing the buck

I fitted a set of tyres on my VW double cab transporter and they charged me R14000-00 for the set.
I managed to get 15000km out of the set which is very excessive wear.
When I took it back to them they admitted to supplying the wrong load-rating Tyre to me and they will put in a low mileage claim to Yokohama and have no guarantee that it will succeed.

They do expect me to pay for a correct load-rating rating set again.
My problem is two fold.
One is that I did not put the incorrect tyre on my vehicle as they are supposed to be the experts.
Two is that I dont see why I should pay for it at all!!
I am prepared to pay for normal wear for the 15000km.
What must I do??