Cracked glass patio door

[danstrak]

Hi all,
First time poster here.
I am looking for some advice as I am not sure what to do next.
I live in a purpose built block of flats (built 1974) I have an Aluminium framed sliding glass patio door, the glass is about 9mm thick and single pane (installed in 1974 )A crack has appeared about a 1/4 of the way up the door which runs from the left hand edge to the middle of the door. I am on the second floor, there are no impact marks. We are trying to claim via insurance but are being fobbed off with everything from, It was caused by thermal reaction, it is general wear and tear, There must have been a stress fratcure when the glass was first made etc etc. Basically the insurance people don't want to pay.
Part of the alluminium frame which grips the glass where the crack starts has been displaced.
I have also just been informed by another neighbour in the same black that exactly the same thing has happened to her sliding patio door (roughly around the same time as it occured to our window (she was away for a couple of weeks and noticed it on her return). It also looks like her frame has moved aswell.
I guess what I really want to know is how likely is it that both cracks are due to thermal reaction?
Any ideas on how we can get the insurance to pay out as our policy doesn't cover wear and tear nor anything to do with the weather.
Thanks,
Dan