Get your lawyers on this now.
Send them a cease and desist right now. Tell them they are not allowed to contact any more of your customers or they will be sued.
You say the list is stolen, let Acacia know that they are using a stolen customer list and tell them to stop using a stolen list, now or they will be liable for any damage they do to your business from this time forward. They should also know that there may be criminal charges if they continue to use a list they know is stolen.
Do it right now.
