Summarize the following:
It's the app that has an image of a small gear inside a large gear. It's the green icon with a white speech bubble about in the middle of the Settings menu. This will prevent any further messages from sent to your Apple account. You should turn off iMessage on all your Apple devices, including iPads, and Mac computers. It's next to the app that has a green icon with a white camera. This will prevent people trying to contact you on FaceTime. You can use any web browser on iPhone, Android, Mac, or PC. Towards the bottom of the webpage, there's a bar where you can type your phone number. A confirmation code went be sent to your phone via text message. Check your text messages to receive the confirmation code. Type the confirmation code in the second line and click "Submit". This will deregister your phone number from iMessage so that text messages will no longer sent to iMessage.

Summary:
On your iPhone, open Settings . Tap Messages . Tap the switch  for "iMessage" to the 'OFF'  position. Tap FaceTime in the settings menu. Tap the switch  for "FaceTime" to the 'OFF'  position. Go to https://selfsolve.apple.com/deregister-imessage/ in a web browser. Type your mobile phone number. Tap or click Send Code. Type the confirmation code and click Submit.