iphone 6 plus - wifi disabled, bluetooth not working, phone freezes & reboots.

I bought a new iPhone 6 Plus about a month ago. Last week, the WiFi & Bluetooth stopped working for a few hours. Basically, the WiFi icon on the slide-up menu became disabled, I couldn't turn it on in Settings. Also, I couldn't turn on Bluetooth in Settings. While this was happening, the phone started freezing which required me to do a hard reset. It also started rebooting for no reason. Then, after a few hours, everything worked fine again. After a few days, it all happened again with the broken WiFi & Bluetooth, freezing & rebooting. Then, after a couple of hours it all worked again (for a few more days). A couple of hours ago, the WiFi & Bluetooth stopped working again, and again it's freezing and rebooting.

When it's happening I've tried resetting network settings, resetting all settings, reinstalling from a backup. None of these worked. But after a few hours the phone returns to normal.

Has anyone else had this issue? Is there a fix? I'm very frustrated right now with this phone!