As long as you are using an unsupported carrier, you will continually get these FaceTime and iMessage activation texts. Either switch to a supported carrier, or sign out of FaceTime and iMessage and stop using them.
2 replies
Contact your carrier as the carrier may offer a blocking service for unwanted SMS from particular numbers.
It is not an iOS issue.
Sms from +44 7786 205094, how can I stop it!