Keep getting an annoying notification: "Your carrier may charge for SMS Messages used to activate FaceTime and iMessage"

I keep getting this notification "Your carrier may charge for SMS Messages used to activate FaceTime and iMessage", which is annoying since I get it like 50-100 times a day.

I tried reinserting the SIM Card, turning phone off and on. I even changed bought a new iPhone and the problem still didn' go away.

Logging out of iCloud greatly reduces the appearing of the notification, but it still happens sometimes and not being logged into iCloud is of course not a long time solution.

I'm looking forward into hearing from you, Have a great day!

Below is a picture of a screenshot done by me, but since it is in italian here is the link for the same problem but in english: https://www.google.com/search?q=your+carrier+may+charge+for+sms+messages+used+to+activate+facetime+and+imessage&biw=1920&bih=941&tbm=isch&sxsrf=ALeKk01EppF2EX5symaNsubyKi9S-cv2Tw:1610997241691&source=lnms&sa=X&ved=0ahUKEwjUpsyymKbuAhXB2KQKHUwECFEQ_AUIESgD#imgrc=MaRXYowy730EiM