GPS issues: iphone 6 will not allow me to turn off GPS functions

Have you checked that there are no Restrictions set up?

Do you have an iCloud account set up with find my iPhone enabled? If so, you cannot completely disable location services without disabling find my iPhone first, in your iCloud account settings.

Is the phone truly yours as in you purchased it sealed in a box at a store? Or is it a corporate/school phone?

If belonging to an organization that has proper IT asset management, the iGadgets can have an MDM profile imposed upon them, in which feature availability can be centrally controlled on a device-by-device basis.

I can see two courses of action:

• Set up, if you haven't already, the iTunes program in a compute (Mac preferred). Configure so it syncs up all apps locally on the hard drive and so it stores the backup also locally on the hard drive and with a password of your choosing. Then sync the device so a backup file is created and all the apps you have populate the Library. When you're confident the full and complete backup is good, wipe the phone clean and Restore from that backup. If iTunes is set up correctly, the "new" phone will be identical and, with luck, the issue resolved.
• Take it to an Apple Store and have them look at it. Note that they may end up doing the same as above, so a backup may also be necessary if you don't want to receive a blank as-new device.

Holler if you need help in setting up iTunes just right. My master iTunes "control center" that contains my whole 580 app collection plus multiple backups of all my iGadgets is at home so I don't have the specifics right now, but it works, no data is lost and you get the bonus of having your valuable junk kept safe.

Well I have done the full reset

Not sure what you mean by "full reset", but you need to restore to factory settings, without restoring a backup (as a new iPhone)

Use iTunes to restore your iOS device to factory settings

Note that this is a Location Service issue, not "GPS", Very little of iPhone location services actually use the Global Positioning Satellite radio. Unless they are outside, with an non obstructed view of the sky, location is done by WiFi and cell towers. "GPS" is not a synonym for navigation or location service.