Dear Sir,
I doubt you will find any sample letters complaining about and wanting to discuss a pay raise you are unhappy with.
Companies can be struggling with the economy - as much as individuals are. I would guess most people are happy enough just to have a job and get - even a small increase.
Telling them you are unhappy with this and feel you are worth more could very well backfire on you. And you could find yourself unemployed in the near future.