American Express Lawsuit Letter

In the American Express Lawsuit letter (American-Express-Validation-Letter.docx), it states that the suit is subject to Michigan law.

" Please also follow Michigan law that states "Verification of the debt or any disputed portion of the debt shall include the number and amount of previously made payments . . ." MCL 339.918(e)(2). As you know being that you collecting on a Michigan debt, you can’t collect or sue me on these debts until you validate the debt and that includes showing the number and amount of previously made payments pursuant to Michigan law. Thank you."

Is that because the 'debtor' lives in the example lives in Michigan?

I live in NJ. Can i quote Michigan law or do i need to find a NJ equivalent?

Amex is suing as a creditor using the debt collection firm of Doyle & Hoefs out of York, PA.

Also, I see responses to Breach of Contract and Account Stated claims but not Unjust Enrichment (my suit has all 3).
In which document can I find that?

Thanks