The message sounds more defensive than agressive. Establish contact with them and try to build a trust relation. Note that they were honnest to inform you at t

The message sounds more defensive than agressive. Establish contact with them and try to build a trust relation. Note that they were honnest to inform you at this stage. This is positive. Try to get a hand on the patent text to see if there are differences in the methods. If one thing is different, then you are safe. Check also about prior art. If your method was described in a document, a manual or somewhere else, it becomes unpatentable. His patent may then be rejected. Don't get scared about it. Investgate and diagnose the extend of the problem (which may be a false problem), know your potential ennemy and see if you could turn him into an ally. He may have a patent, but you may have a business. It is the execution that matters. But evaluate the risk and odds to lose ground. If you had some innovation, you should patent it, or publish it to make it unpatentable. You may publish it in patagonia to make it prior art to blow a patent troll if one shows up and keep your sauce secret in the place where you develop your business. Patents are not expensive if you write and fill it yourself. I did it here in France and it costed me 280€. It did took me some time to learn how to write a patent, what to be carefull about, but it's not that hard.