Bad Service

My car went in for service on the 16/07/2015, service was running late due to the fuel filter not been available on time. Fuel filter was changed and received my car that afternoon. As driving home the car starting jerking and misfiring. Got home open the engine bay and noticed that it was washed, so could have been some water in the spark plugs. Tested next morning again but problem persisted. Took it back to Toyota Kingsmead Durban, they tested everything and then told me that one fuel injector was blocked. It will cost over R2000 to change this injector, the problem is that the car was fine when it went in, also by their fault some dirt got in to the fuel line and blocked the one injector., so why is this at my cost. This needs to be taken care by the dealership cost not mine. Car Registration number BF12XNGP.