Your house would have to be foreclosed on it could be sold or you could be asked to move. And it cannot be foreclosed on without providing you notice and a chance to respond. If it hasn't been foreclosed on, you are under no obligation to leave. You could check with your county clerk to verify that you still are the owner; if ownership of your house has been changed in the official records but you were never given notice, it may have been done improperly and you should get a lawyer to challenge it.
You can also contact the person or institution sending you the notice and explain to them that you are still the owner, so they cannot ask you to leave--that gives them a chance to try to provide any evidence that ownership has changed.