Locked Phone / Forgotton PIN

[WexIan]

Hi there,
Recently went back to a S7 from a HTC M9 and wow what a difference and love this phone now. When setting up phone from new I set up a PIN and fingerprint screen lock. All was going well until I recently restarted it as had it turned off, now after a restart you have to re enter your PIN for fingerprint sensor to open it but unfortunately I was unable to remember my PIN ( silly bugger next time write PIN number down ). Eventually I opened it using Samsung Find My Mobile by using Lock My Mobile and using a new PIN phew what a relief as I didnt want to do a factory reset and then have to reload everything. Now I want to change my PIN to a new number ( already written down ) and when I go into Screen lock type in settings and it asks me under Confirm PIN to enter my PIN I enter the PIN I used in Lock My Mobile to open phone it doesnt accept it and locked me out again for 5 minutes but after that time fingerprint sensor opened phone normally. Question is how do I reset a new number because if I have to restart /reboot phone for any reason I will be locked out again.