How do I fix the drafts surrounding new upvc windows ?

I had new UPVC windows fitting in the whole of my house approx 2 years ago. They were great for the 1st year but now we are getting drafts around the window frames, wind whistle around the frames. I thought that the installers had put expanding foam to seal the gaps between the UPVC frame and the brickwork but upon closer examination, it appears to be sealed/weather tightened using mastic beading and it is this that is being used to keep out the elements. In some areas the mastic is 10mm – 20mm wide and it is coming away from the sides showing a gap which I believe is causing the draft and creating a cold barrier. Is there anyone who knows whether just using sealant is a correct method of installing windows ? I have asked the company to fix it and they say that I must pay if I want the apparent gaps filled. I did also explain that even sound gets through…. You can close the window and you can hear the noise outside at the slightly reduced level than when the windows are open. Is there an independent body I can go to & get independent advice. Any help would be really appreciated. Cheers MIKE