An attorney will say "It depends." You are describing a number of potential issues and depending on the specifics, these issues raise to illegal conduct. Depending on where you are living (in Portland, Multnomah County, or???) different rules apply. Although you are in Oregon and State rules will apply--often local rules provide more protection for rentors/lessors.

The amount of time you've been staying at the property will also matter. As with the letter you received from the attorney. You deserve to feel safe in your home, and even without a written lease (which is always a very good and important thing to have) you have certain rights. If you feel unsafe or threatened you should call the police.

Situations like the one you've described are challenging because it is often your words against someone elses--that doesn't mean you don't have claims or that your claims aren't legitimate--not in the slightest. Instead, it means keeping records of everything that has happened is very important. Just like it is important to keep copies of everything you receive.

The exact details here make all the difference - which is why it is ALWAYS a good idea to only rent pursuant to a written lease. One main issue for you is likely to be what exactly it is that you rented. A written rental agreement specifies that. Here, IF the landlord can make an arbitrator/judge/jury believe your rental did not include the shed and land it sits on, then he still had a right to use it for his own purpose though residential use likely violates local health, zoning, and other potential laws. IF he tries to live there again, by all means file complaints with your local government agencies. Save the letter from the attorney - depending upon WHEN it was issued, it may be unlawful in and of itself. IF you have been there less than a year, and the rental is not within the Portland city limits, you likely are only entitled to 30 days written notice to terminate your tenancy. If, however, you happen to be within the Portland city limits, then you are entitled to receive at least 90 days prior written notice, relocation assistance notices and perhaps payment, etc. Beyond all this, they may have "extended" your move out time until June 30 but it is not at all clear at the moment whether the court will enforce any such notice, given the Governor's eviction moratorium currently expires June 20. But what then? The point of requiring such notice is to give a tenant time to find a new place, orderly pack and move - precisely what has been denied by the shelter at home order. So if the Governor's Order is in effect until June 20, you would only have 10 days to accomplish what you are otherwise supposed to have 30 days or 90 days to do. So I personally doubt a Judge would throw you out for not being gone by June 30 but there will be a lot of people in the same position and I suspect that the court's or Governor or state legislature will issue a policy decision on this and related matters before June 20 gets here. But it is just my guess - and who knows what they may actually decide. All told, particularly if the landlord has an attorney, you may want to review everything with a local landlord-tenant attorney yourself to at least determine your exact rights and their timing; perhaps to even discover whether you have valid claims against the landlord. Good luck.