Rejected claim

Never have I ever had such horrible service. My car went in on the 14th of November, they sent me a rejected claim letter today. The fault on my car, was there before I purchased it at We Buy cars, I had it for 2 weeks and it overheated, no oil in the car and there was a crack in the engine cooler tank.. Innovation says it is due to my lack of maintenance. How the f??? We Buy Cars told me it had been for roadworthy and had been for a pre sale service. Worst companies ever.