At the very least ask them to oblige with the terms of the NDA immediately. Formally ask them, using the official communications methods and cc with email, to

At the very least ask them to oblige with the terms of the NDA immediately. Formally ask them, using the official communications methods and cc with email, to return everything to you and to verify to you that they have not distributed them to anyone else and that they have destroyed all existing copies. Do it ASAP. Formally request that they do not use information they have acquired from you under the NDA in any of their businesses. This is pretty standard stuff for a decent IP lawyer.