If there were two witnesses to testify against you, they may have conducted the JC in abstentia and made the decision to disfellowship you. If they went this route however, they would have supposedly notified you verbally and advised you of your right to appeal the decision within 7 days. Since evidently you were not contacted, I would suspect that the official stance is that you have disassociated yourself by your actions or statements in your letter--you have made clear that you do not want to continue any association with Jehovahs Witnesses. No JC, no 7 days, etc. Thus, if an announcement was made to the cong it was "Hoggieman is no longer one of JWs." Yes it's the same announcement either way.
Can you sue? Sure. Anybody can sue anybody else. Can you afford the lawyer? Even if you can, is it worth it? If you sue on the basis that they had no right to "harrass" you after you had already made clear that they were to leave you alone, will the court/jury agree that the announcement (if there was one) constitutes harrassment? Did it go beyond the religion's 1st amendment protection? If so, do you have any damages? What were they? How much is that worth?
If you win, WT will supply legal counsel and see that this kind of anomaly is appealed, even though they will not want to be a party to the suit. Can you afford the lawyer to go through the appeal? Maybe you could get lucky and the ACLU would take your side on it. But maybe they'd take the WT's side. If you win, it's going to become a serious 1st Amendment case and there would be lots of players wanting to be involved, most all against your position.
NOT a lawyer here, so maybe someone who is will comment. Band On The Run?