How to get rid of find my iPhone 30 day grace period

I was having trouble resetting and taking off Find my iPhone as I was trading in my old phone with apple and it kept saying it would have a grace period of 30 days until the function was completely off the device. I reset and set up again the phone and then rather than going into the Find My app I went into settings and turned it off that way then erased all data. When I went on my new phone Find My app my old phone is no longer visible in devices.