You should have went directly to the airline desk,explained the situation and it would have been replaced(if it was a big airline)then and there.Stacks of cases of all shapes and sizes are held there,if not your brand the exact one would have been found.Once youv'e left i don't think you have a leg to stand on,i doubt this is covered by your travel insurance.
I did consider this at the time, but there was already a big queue at the desk and we were knackered after a long flight. I knew we had a guarantee on case and assumed it would be replaced.