?

I live in Oregon as of September 30th my 6 month lease we have expired. 6 weeks ago my roommate/ partner notified the office, verbally that we intended to move out as soon as our lease ends. There is a provision in the lease requiring we provide 30 days written notice. However, upon further review that page of the lease was never signed by either of us. The landlords policy is once a lease is up the tenants automatically revert to month to month tenancy until such time they give 30 days notice. We notified them on the 18th verbally of our intent to move out, which they then counted. We had planned and prepared to move out this weekend. Much to our surprise a notice on the the door stated we were bound as renters under a month to month policy until the 17th of October. At this point we know we messed up but didn't realize the lease had a 3rd page, at which time we would have read it. Needless to say the landlord wants to collect that rent. So much so that when I went to the office to ask to simply view the lease or a copy of the letter we had been sent, as my roommate had filed it, the landlord became increasingly rude.

"Haven't you ever rented in Oregon, you HAVE to give a 30 day written notification, no matter what"

What I'm wondering is what is the premiss for this, I've been told upon the completion of a fixed term lease should the tenants continue to reside they would be considered a tenant at will, until they sign a month to month or another fixed term lease.