What can we do legally with this vendor?
Anytime you are asking for legal advice - you need to talk with your legal folks. However, based on the limited details provided - i'm going to make the following assumption and my thoughts -which are the following:
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1. You bought or are trying to buy the items from the dealer NOT the Manufacturer.
My thoughts - I would escalate this to your supervisor and have them talk with their counterpart - somtimes this can resolve the issue. If it doesn't work - talk to your legal folks and follow their recommendation.