If you restored the phone from backup, I would try to wipe it and test connectivity with a clean device. If you did not restore and the device is set up as new then I would recommend a trip to Apple to swap it out. The BT radio could be having an issue.
In case you have your iPhone 7 restored from the iPhone 6 backup:
You will have to forget every device in Settings > Bluetooth and start a new pairing as if both devices were pairing for the very first time.