A lot of the people who are responding to you in this thread and upvoting comments in this thread have no idea what optima is. Your dad is right. It's questionable whether optima is actually worth the $4k you're paying them, but you've already paid $4k to retain a professional who deals with situations like this on a day to day basis. Let them deal with it, they'll do a better job than some armchair redditor who thinks that they'd be able to sweettalk the IRS into ignoring a debt.