Blurry windscreen bought from Deans Motor spares. No responsibility from sales people

Horrible service ever from Deans motor spares( Midas deans) I bought a windscreen that has a layer of what seams like plastic of some sort that won't come off. A day later after trying to clean it off I took it back to show them what the windscreen looks like and they 1st blamed it on fitment, after I advised them that they fitted it for me the reason changed to me not having the slip. I then produced on my cell phone the proof of purchase that had their details on and they said it wasn't proof enough. In the 21st century where paper goes missing I'm 200% sure that they could have gone into their systems to check for that transaction that was done 2 days earlier. And all I received was a no we can't help. Shocking to say the least, and for this institution to be part of the Midas group.