Samsung S7 GoPhone unlock denial

Last March, I purchased a Samsung S7 Edge to use with my GoPhone account.  I bought the phone outright; I use the automatic payment system to keep my plan active.  Looking to upgrade to the S8, I wanted to have my phone unlocked to increase it's value when I sell it after I purchase a new phone.  Going through the automated unlock request system, I requested an unlock, which was subsequently denied for "not having an active paid service for six months".  This phone has been active for the past year, and I continue to use it until I purchase my new phone.  Why was I denied?