How can I sue someone who is selling my patent product?

Call a Patent Litigator and file a suit in Federal Court.

The first thing you should do is to send them a cease and desist letter. This will prompt them to stop or hire a lawyer. A letter like that should not cost more than $800. This letter needs to be carefully drafted in order to avoid a declaratory judgment. If this doesn't work then you should carefully analyze the case with a patent attorney. Patent litigation is expensive and a lot of due diligence needs to be done before filing the suit.