To clarify, if you use iMessage and faceTime your phone will send texts to Apple’s servers in the UK any time the phone gets turned off or on, and also regularly during normal operation to reconfirm that these services are still on. You have 2 options: Switch to a supported carrier that doesn’t charge for these messages (or even show them) or permanently disable iMessage and FaceTime. Unless you want to pay for daily international text messages to Apple’s server in the UK you should log out of FaceTime and iMessage. Note that turning them off is not sufficient; you must actually log out.
FaceTime: Go to Settings/FaceTime, turn it on if it is off, tap on your Apple ID and tap Sign Out
iMessage: Go to Settings/Messages, turn it on if it is off, tap on Send & Receive, then your Apple ID, and tap Sign Out
Two more international texts will be sent after you do this, but they should then stop.