What must I do if I break my oath after swearing: "By Allah Almighty, if I break my oath, I owe a thousand oaths," and my intention was to expiate this oath with a thousand expiations?

If he broke his oath, he owes two expiations: one for the first oath, and one for the oath of contention, because the second oath took the form of a vow, and its dissolution requires an expiation for an oath.