Landlord sold the house tells us to pay someone else. illegal?

My bf and I live in a 2 story unit. Our landlord and his family used to live under us. Our lease isn't up until June and they randomly up and left, moved somewhere. Without notifying a single person. The "new owner" gave us a letter in the mail telling us to write the rent checks out to him and put... show more My bf and I live in a 2 story unit. Our landlord and his family used to live under us. Our lease isn't up until June and they randomly up and left, moved somewhere. Without notifying a single person.
The "new owner" gave us a letter in the mail telling us to write the rent checks out to him and put it in the mail box. Never met him... never changed the lease. For all we know the lease contract is still under our first landlord.

Should we do something? I'm going to email this man and ask. But don't we need an updated contract??? Also for all I know this could be a random con man trying to take my money! Please help and thank you!

P.s. we live in Chicago, IL.
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