“Their presence in heaven is frequently confirmed by miracles: and that would be God’s own testimony.”
Satan also can perform miracles, so it isn’t wise to rely on such things as testimony from God. Better to rely on the certain testimony contained in God’s Word.
Satan doesn’t perform miracles that glorify Our Lord Jesus Christ. Satan can’t stand Christ. Can’t stand Christian religious observance. Can’t stand the Cross or Holy Water, or even anything symbolic of the Deity. That’s well known.