Whilst cooking the glass of our smeg oven exploded into thousands of little pieces?

The oven is 18months old so 6 months past its warranty. They have offered to replace the glass for free (£45) whilst i pick up the labour price (min £75). I think this is not on as you pay over £1000 for an oven like this and its not due to wear and tear. Also the fact that we had the children in the kitchen when this happened and could have been nasty.
Can anyone offer advice on what to do next?