I sent a company a 1099 form which was a corporation and should not have been sent. They just informed me 5 months later. Now what do I do? How do I retract a 1099 ?

Issue a corected version of the 1099 with $0 amounts. You will also need to resend to the IRS with form 1096. See: General Instructions for Certain Information Returns (2014) (http://www.irs.gov/instructions/i1099gi/ar02.html#d0e822)