Skylight is leaking but neither insurer, loft fitter nor previous owner accept responsibility: where do I get redress?

I purchased my house in December 2006 and had the time had all the standard checks done on the house. In approximately October 2007 the window in the loft, which is a skylight began to leak. I rang my insurance company to see if it could have been caused by storm damage. A surveyor came out from the Norwich Union insurance who advised me that he believed the problem was caused by the window and he could not seen any physical defects with the roof. I requested a second surveyor to come and assess the problem and he also believed that the leak was coming through the window (flashing kit). I rang up the previous owner to inquiry if she had ever had any problems with the window. The loft conversion was carried out in 2003 and the previous owner assured me that she had never had a problem. She also told me that the work was still under warranty as it had a 6-year warranty. I rang the company (Topflite) who carried out the work on the loft conversion but they told me that the warranty was only available to the previous owner and was not transferable. One of the manager's from Topflite said he would come out to assess the damage and see what the problem is. I have been calling him since October 2007 and he has continuously ignored my calls. I feel very disappointed about the leak in the loft because it has caused a lot of damage to the walls and carpet. I am concerned why the problem was not detected when the checks were done on the house before the purchase. Please could you advise me on what I can do?