My credit has been deducting automatically by sending sms by iMessage

They are listed here as a supported carrier: https://support.apple.com/en-us/HT204042

If they are charging you for iMessage/Facetime activation messages, they should not be. Contact them again and ask to speak with a supervisor if needed.

~Lyssa

And both of us have explained what you need to do. Contact your carrier about why they are charging you, as they shouldn't be, and if you do not wish to use iMessage and/or FaceTime, you need to log out of them, not use turn them off.

As I responded to you in your other thread about this https://discussions.apple.com/thread/251249489, it is probably the activation SMS for iMessage and FaceTime. Your carrier is charging you for that. While the message is from your iPhone to Apple, it is not Apple charging you, it is your carrier.

Are you seeing messages sent to a number that starts with +44?

If so, what country are you in? What carrier are you using?

~Lyssa