I have to agree with PA.
The harsh truth is your employer owes you NOTHING but pay for the work you have performed.
The liberating side of that is, you owe them NOTHING but 100% effort for the job you have been hired to do.
I would suggest not writing a letter. Have a conversation. Things in writing tend to be permanent and can "grow legs" within an organization.
We have all felt wronged by our employer at some point in time (sometimes often as in PackRat's case).
