call your lender and make sure that your mortgage has indeed been sold. Until you get a letter from both lenders advising that your loan has been sold (or assigned), you should continue to pay the first lender. This is a problem now that so many banks and lenders are having to close their doors, but also opens up the door for new scammers to try and collect mortage payments from the unsuspecting homeowner.
When in doubt, make the call!