A. Loren,
Read that offer letter again carefully and look for any disclaimers. If you see none, I wouldn’t be shy to call them back and tell them that you expect them to honor the offer and when they refuse, ask them how that letter could be considered anything other than bait and switch. If they can’t point you to the disclaimer, or have some other excuse that doesn’t pass the smell test, then tell them that you will consult an attorney that is knowledgeable with bait and switch.