This has happened to us on a cooker that was only a year old.....the glass was not removed but cleaned in situ...it then all of a sudden smashed.
I googled the make of the cooker including model number, found a supplier who overnighted the glass, delivered direct to the customer and they fitted it, just in case
Total cost £65...profit from job out of the window, but both sides happy....lot better than a new cooker...think they are trying it on.
Do your best to locate a glass, then take it round to the house,it's up to you if you feel brave and offer to fit it, not a lot more they can say if you replaced the broken item at your expense.