so, here's the story

I booked some tickets in December to travel in January which I cancelled 5 dies later. I couldn't travel due to a death in my family.
I paid by Visa so I claimed the money back on my Visa insurance.
My Visa insurance have paid me back the money for the 'tickets' but say they are not liable for the flight taxes and charges.
The charges are fairly insignificant (less than £100) but the flight taxes amount to more or less £600 - getting on for half of what I shelled out.

So my question is this;
if we didn't travel where did this flight tax/ airport tax money go and how can I claim it back and from whom? Has it just been pocketed by the travel agents? Are they obliged to refund me taxes ?

anyone got any experience with this? I can't really afford a £600 - £700 hit to my finances right now :(