Guarantee from Duramaster is not what they advertise on their documentation

We used Duramaster to install canvas on our patio - 2 sides at first. Shortly after we closed of the 3rd section in 2018. Mark was exceptional at selling his product as per previous installation and as they claim to have a 5 year guarantee on canvas and clear pvc we made use of the offer (even though they were not the cheapest by far). Shortly after this installation the clear pvc started changing to a yellowish colour. We wrote it off to maybe that side being in full sun most of the day - no questions asked. My bad...... In November 2020 I noticed what looked like plastic on the outside of the patio. As I started to investigate I saw a whole in the pvc. I phoned Mark and asked for a replacement quote as he informed me that the insurance should cover the damage. They off course do not as they reckon it is due to perishing....which falls well into the so called warranty offered by Duramaster. So, when I asked Mark about it he was looking for all sorts of excuses i.e lawnmower striking rocks (in fact this area walks out onto a deck....no lawn near). I found his replies to me condescending and arrogant. What bothers me most is that he did not even bother to come look at his product that he so boldly selled in 2018 and possible causes for the damage. In fact, I never heard from him again after questioning the quality of the pvc they installed. Strange that none of the other windows which was in fact installed before this one shows discoloration. Be very careful as all is not what it seems when it comes to Duramaster's guarantee......