Am I obliged to fulfill the oath I took not to perform Hajj through the Ministry of Awqaf, knowing that I had performed Hajj previously and had doubts about the validity of my standing at Arafat?

The question is unclear. If the questioner swore an oath not to perform Hajj with the Ministry of Endowments and now wishes to perform Hajj with them, he may expiate his oath and perform Hajj with them, as the Prophet, peace and blessings be upon him, said: "Whoever takes an oath and then sees something better than it, let him do that which is better and expiate his oath."

However, if the question refers to his doubt about his standing at Arafah in his previous Hajj after completing it, then this doubt is invalid and has no bearing, because doubt after completing an act of worship does not affect it, and his standing is considered valid.