Implied/Month-to-Month tenant's Improper Termination Inquiry-WI.

[John Joey]

I have a question for the landlords/lawyers regarding implied lease/short term lease termination. I think I know the answer, but I'd like confirmation.

A tenant informed me of their vacation today 10/31, and stated that they'd written a termination letter. Reviewing my effects, I discovered their letter in an envelope from "Atos Medical." Although the letter is dated 10/1/19, it neither contained my address nor any sender information. So, it was among my trash.
I believe this notice is inconsistent with landlord/tenant law as cited in statute 704/21/2/C, because it wasn't registered, and inconspicuously packaged.

Am I within my rights to; decline this notice, request November's payment, and an 11/29 effective date? If so, how shall I proceed if they refuse to pay?

Thanks!