Notice in the mail about your property? Here’s what to know

Say you get a letter that seems to come from a bank. It says it’s related to your property, has the words “FINAL NOTICE,” printed on the letter, and has what looks like a refund check attached. Your first thought is that you’re getting money. But then you notice there’s no signature, and the small print says it isn’t a check. The mailer says to “Call IMMEDIATELY”. But what happens if you call?