If they refuse you can escalate or hire a company that will negotiate for some percentage of profit. In most cases I had this problem they gave me a refund, but sometimes I had to argue a bit.
I used to work at one such company. The process can take a long time but it is mostly hands-off for the traveller and success rates are high once the case has been taken.
Edit: and also, these claim-assistance companies work on a winning fee.
