Airplane mode is not working on iPhone 6s

Same thing for me only the call was from an HTC phone not an iOS so I'm pretty sure that it wasn't voip. It was a regular call. I also received green texts while in airplane mode many times during the night.

Being from an iOS phone makes no difference. It all has to do with your carrier supporting wi-fi calling, and your phone being set up for it. If you have wi-fi calling set up with your carrier, then you would receive any calls to your cell number if you are connected to wi-fi. This is an enhancement to cellular networks to help those users that may have poor cellular reception in certain locations.

The issue regarding SMS is difficult to explain, as I'm not sure if the wi-fi calling will support your receiving SMS in that manner as well. I'd have to defer that to someone that has more experience with wi-fi calling. But wi-fi calling is a feature the iPhone will support if your carrier supports it and you have it configured on your phone.

Do you happen to have a carrier that supports Wi-Fi calling and you have that activated? Do you see the Airplane in the upper left of the status bar when you turn on Airplane Mode?

Glad you got it sorted out.