Ponthieu resists your army of invasion. Count Guy is determined to make you bleed before he will allow you to take his prisoners. That is payment of a sort; but he would prefer money, lands or titles, or all three. You can continue this stupid war, or allow that you made a mistake, swallow a little humble pie, and meet with count Guy to discuss terms.
Keep fighting until you beat Ponthieu into the ground; the county is no match for your might.
Parley with count Guy. Work out terms for ransoming Harold Godwinson.