Do NOT Respond! in any way!!!.
Send the Chinese NOTHING AT ALL, not even a polite “no thank you”.
If you do, you will find your patented product suddenly being knocked-off and sold under a very official-looking forged “license” using the same signature you foolishly put on your “no thank you” letter.
Sure, you can sue, and sure, you can stop them from importing into the USA with a lot of time, trouble and money (via trademarks more readily than patents) but this all takes time and money, and in the meanwhile, they are still counterfeiting your product, and selling it to the EU, Asia, etc, where your patent enforcement options are even MORE expensive, if you have any rights at all.
Trademark and copyright are far more powerful tools to control pirates, and trade secret agreements are far more powerful ways to control a 3rd-party manufacturer. And NEVER have your complete product fabricated, logoed, and boxed in the same facility, as they will simply run a 2nd shift, and sell your stuff out the back door to unethical wholesalers at far lower prices than you can.
The parable here is the one of the famous cartoonist who, with advancing age, hired a writer to create the stories in his style. Then he hired an artist to draw the strips in his style. Then he hired a colorist to color in the panels. Then he hired a captions guy to do the lettering of the captions in his style. And he never let ANY OF THEM know of the existence of any of the others, and they were all subject to very strict non-disclosure agreements, so they never told a soul. He hired a secretary to handle the mailing back and forth of scripts and sketches, and he retired to a beach.
The comic strip continued to run for a full month after he died before anyone realized he was dead.
Any level of security less than this with any 3rd party subcontractor will end in tears.
If you want to license, license to a USA entity that is NOT a DE or AZ LLC, so you know the principals by name, and make them responsible for counterfeit enforcement, planet-wide, as a condition of the license. Make them go get all the trademarks in all the 3rd world nations.
Patents are a license to go bankrupt on legal fees chasing pirates who have no visible assets, who will simply disappear and reappear under a new name when you finally get a default judgment against them.