Well, this is really more a question for the Business & Marketing pasture, but here goes:
In a strictly “legal” sense you have every right to go after them for violating your copyright, although your best target would be the other production company as well as the former client. But, in a practical sense, is pursuing this worth it??
Do you have a contract with this client that specifies that you retain ownership of the footage? Has communicating this been something more than a conversation you had?
Your description basically says that this client has moved on from using you so there is little you can do that won’t consume a LOT of your time AND MONEY in legal fees. You could probably get a lawyer to write a “cease and desist” letter for not a lot of money, but, should it be ignored — which is fairly typical — you could be looking at tens of thousands of dollars to go the litigation route and have no guarantee that you’ll win and be able to recover the legal fees as well as any damages.
Long and short of it is:
a) make sure that the other production company is aware of what this client has done and
b) do what you can to embarrass the client making it POSSIBLE that they will right this wrong.
Just don’t count on it and remember that even though you are in the right, your risk is harming your reputation and being known as someone who is difficult to work with.