Is the delay penalty ruled by the judge in a debt case considered usurious interest (riba), especially if the debtor believes that taking it is an injustice to him and an increase upon the money he was loaned?

A late payment penalty that goes back to the creditor himself is forbidden and outright usury (riba). As for a penalty that goes to charitable organizations, there is a difference of opinion among scholars regarding it, with most of them considering it forbidden. Your father's view is correct, for a judge's ruling that contradicts Islamic law is not to be relied upon, and his ruling does not, in reality, make what is forbidden lawful or what is lawful forbidden, even if it is outwardly enforced. The judge rules based on outward appearances only, and the one in whose favor the judgment is made must seek what is lawful, for the Prophet, peace and blessings be upon him, said: "If I rule in favor of someone concerning the right of a Muslim, then it is but a piece of fire, so let him take it or leave it."