How to cancel 3.99 charge

If you mean you've subscribed to something that you no longer want to auto-renew : How to cancel a subscription from Apple - Apple Support

If you mean get a refund then purchases are considered final as you know, but you could try the 'report a problem' page to contact iTunes Support and see if they will refund you as a one-off : http://reportaproblem.apple.com

Or you can try contacting iTunes Support via : http://www.apple.com/support/itunes/ww