How do I repent for the zakat on my money that I did not pay when I was not praying, and do I make up for it for all the past years, or does repentance supersede what came before it, especially since I now own nothing?

One who abandons prayer out of laziness and then repents is obligated to pay Zakat for the past years in which he possessed the nisab, even if the wealth has been destroyed, because he neglected to pay it, and it remains a debt upon him. As for one who abandons prayer out of denial of its obligation and then repents: if he was excused by ignorance (such as a new convert to Islam or one who grew up in an ignorant environment), he must make up for the missed prayers and Zakat. If he was not excused, he is considered a disbeliever due to his denial, and the majority of scholars hold that he is obligated to pay Zakat after his repentance. To make up for missed prayers, one should perform as many as he can daily. If he cannot determine the exact number, he should pray what he believes to be the predominant number. For Zakat, he should pay Zakat for each year according to the wealth present in that year. If he cannot determine the exact obligation, he should act with caution.