How do I get my iPhone 6 to revert back to using WiFi rather than Cellular Data?

[iMore Question]

Recently, I was trying to connect with another iPhone user while away from WiFi. The iPhone asked me if I should send the message as a cellular data message, and I said yes. Now, all of my messages to my friend are going as cellular data, even when I am at home and connected to home WiFi AND I have my cellular data turned OFF. How do I revert back to using WiFi rather than my cellular data? I tried turning off my WiFi connection, and I turned off Cellular data, but it is still sending as cellular data.

 

[Rob Phillips]

Welcome to iMore! What indication are you getting that your messages are sending over cellular data and not wifi? The only thing I can think of is that you have a weak wifi connection and you have Wi-Fi Assist enabled. Go to Settings > Cellular, then scroll all of the way down and toggled off Wi-Fi Assist.

 

[bhsia]

Thank you, but no. That is already turned off. I have also turned off Cellular data, SMS messaging, and MMS Messaging for good measure. The iPhone refuses to revert back to using WiFi.

Any other ideas?

 

[bhsia]

The indications are quite clear:
1) I get a pop up message that tells me how much my cellular account has been charged for the outgoing text message immediately after it finishes sending!
Essentially, "Cha-ching! Your iPhone's refusal to use your home WiFi has cost you another $.##. Your account balance is now $#.##."
2) The outgoing message, when it finishes sending, is in green, not blue.