Insurance claim rejected

I had a claim regarding the suspensions for my land rover which Discovery Insure resolved. They had insisted that we need to use their service provider to do the job which we then gladly obliged. After getting the vehicle back the water task started to fill up with oil. We had informed Discovery of this, who advised that we take the car for a check up somewhere. It appeared that in order to fix the suspensions the mechanics would have had to open up the pipes the air pipes and reinstall them. The filling of the oil in the water was due to this mishap as it was done done thoroughly. The quote to resolve this mess is +-R30K which the discovery assessor seems to think is resultant damage!!! which they do not cover!!!...IT IS THEIR OWN SERVICE PROVIDER SO WHO'S FAULT IS THIS ?