This is very confusing. I'm wondering two things:
1: why do you have to apply for a citizenship you already acquired through birth?
2: why would being married to your ex husband for over three years, when he obtained the citizenship through you, have anything to do with this?
It seems that you are already an Italian citizen, as you were born with it. I don't see how you could have renounced that citizenship in any way if your ex husband acquired it through you (unless your other marriage forced you to renounce, or you naturalized somewhere else). Even in that case, wouldn't it be easier to go back and live in Italy until you can apply there?
All in all, it sounds like you still have Italian citizenship, and all you have to do is apply for a new passport.. ?