As my claim draws to a close, I would like to take this opportunity to express my gratitude for your hard and diligent work but most of all for your patience. I realise that I have not always been a delightful client; I have often been short-tempered and impatient, sometimes even downright unpleasant.
I know that you were just doing your job but I thank you for doing that job with a calm and professional manner and I thank you for trying so hard to make a frustrating and difficult process go as smoothly as possible.
Many Thanks.