Similar thing happened to me. is the address on your DL same as the one you live at?
Mine wasn't, the postman knows my buisness address and dropped the reg letter around, it was signed by someone else. Anyhow, my offense was a 1 point offence, but when i went to court to explain what happened, my solicitor was asked, is your client pleading guilty to the offense or not? I pleaded guilty but with migating circumstances, to cut a long story short I was fined €100 euro. Since the court has nothing to do with points, thats the RSA, the judge never mentioned points. Low and behold, a month or so later I received notification from the RSA that I had been found guilty in a court of law and my 1 point offence had turned into 3 points.
My only regret is not going to court and defending myself, I would advice you do that, the judge may throw it out.