iphone – Why imessage and FaceTime continues to charge money even after activation?

It’s been 2 or 3 months that I used to get alert from my carrier that a amount has been deducted and I couldn’t find what those charges were for. It’s today so happened that the alert of deduction and Apple ID verification came simultaneously and that directed me towards imessage and FaceTime. With a few google searches I found this Apple Support link very helpful, in that forum it written clearly

Depending on your carrier, it can be normal for the activation of iMessage and FaceTime to involve incurring a cost for sending an international SMS message.

And when I searched for the cost of international SMS in my country and carrier, it was same as the deduction amount that I got alerted for. So, now it’s clear that my Iphone 7 is sending international SMSs for the activation of imessage and FaceTime (which I say is already activated). Now, I have two questions:

  1. Why it is sending those international SMS even after activation is done?
  2. How to stop it? It has already cost a good deal of deduction.