Defamation can come in the form of slander or libel. And, one of the requirements for a successful defamation claim is that the defamatory statement be communicated to some third-party. In your case, the statements that you claim are defamatory were stated in a letter that only you and your former boss have seen. So, based on the facts you have provided, you would not succeed if you were to sue for defamation.
Now, as for suing for your paycheck, generally, an employer must give a fired employee their final paycheck immediately.
No, you would not have a viable case for slander, libel or defamation.
However, you have a claim for unpaid wages and for waiting time penalties. See:
Frank W. Chen has been licensed to practice law in California since 1988. The information presented here is general in nature and is not intended, nor should be construed, as legal advice for a particular case. This Avvo.com posting does not create any attorney-client relationship with the author. For specific advice about your particular situation, please consult with your own attorney.
Consult with a local employment atty. You might possibly have a claim for wrongful discharge, depending upon the type of employment you had, etc. You can file a claim thru the Labor Commissioner's office for wages and accrued vacation pay, along with penalties. They are supposed to pay you immediately upon termination.