It is irrelevant that you invented something 20 years ago and can prove it. The US no longer grants patents to the first to invent something and instead has joined the rest of the world in granting patents to the first to apply for one. Furthermore, if you didn't apply for a patent 20 years ago, you would be considered to have abandoned your rights in the invention. Thus, you have no rights to enforce and do not need a lawyer to enforce nonexistent rights. However, if this other party obtained a patent on your invention and you can prove that they got the invention from you, you may have an action to obtain their patent and should consult a patent attorney.
Answered on Jan 05th, 2015 at 1:04 PM