It depends on what you paid. If there was interest and attorneys fees, and you didn't pay those items, you didn't pay the debt. Likewise, Plaintiff...

Since nobody online can read your contract, or anything the owner has sent you, it's impossible to give an answer that you can act upon. I suggest...

Certified letters are not signed for. There's no reason to believe that it did not send you the letter, merely because you didn't receive it. Mail...

Its a scam. Ignore it. Do not contact them and do not send them any money.

Nobody can do that here, but you can hire an attorney in your town to help you.

This is a legal issue, so you should consult an Illinois attorney with the notice and your lease

They can sue you and obtain a judgment, and possibly garnish your wages, bank account, and take personal property. Hire an attorney.

You have the choice to stay until your lease expires, then move. The new owners can raise the rent consistent with the terms of your lease or...

This seems to be a running commentary, but not a question. Do you have a question?

You don't have a case based on these facts.