What must an individual do after breaking his oath and returning to the disobedience that he pledged to Allah to abandon, and will his prayers or fasting be accepted after he said: "And if I do it, O Lord, then do not accept from me prayer, nor fasting, nor anything"?

You must offer sincere repentance for the sin and not return to it. You also owe expiation for breaking your oath, which is: feeding ten poor persons, or clothing them, or freeing a slave. If you are unable to do any of these, then fasting for three consecutive days is more prudent. Strive to ask Allah to accept your acts of obedience, for your prayer of non-acceptance is a grave error.