Holiday in Corfu

Complained about my holiday in Corfu this year as the accomodation was very poor, the holiday rep agreed, official complaint was done on holiday, complained everyday but it took them ten days to move us?

Wrote my first letter to Thomsons on my return, which they returned, apologising with 80 quid in travel vouchers (Holiday was £850).

Wrote to them again, and they ignored my letter.

Contacted ABTA who told me to write again.

Wrote agian and Thomsons said they 'could never please me' and this was the end of our correspondance.

What should I do next, is it worth going to arbitration?