lobster
Post missing.
In the UK we have (optional) legal cover, which tends to kick in in these sort of circumstances. Do you have such a thing? A lawyer may succeed in kicking them into action.
Otherwise, it seems pretty cut and dried. If they are unwilling to repair your bike(which seems to be the case), they will have to replace it. So total it...
Sorry for your situation. This sort of thing always sucks.