I suppose it depends on a few matters.

1. The exact wording of the warranty.

2. The cost. If it was a small sum, is it worth the grief ? Only you know what is a 'small' sum though.

Always worth going through an appeals process, with a threat of going to the ombudsman sitting in the background (warranties are these days viewed similarly to financial products, with regulatory bodies, etc). The warranty Co. should be able to tell you how to appeal a decision, it should be in your papaerwork.