I am receiving international sms charges that I have never made

No, it is send in the background to make connection and is not recorded in your normal Messages app but your telco (or your bill) can tell you which number it uses.

Is this number# 00447786205094 used?

The number is Apple iMessage & FaceTime activation server in England.

Apple uses an International SMS to activate your phone number with iMessage server.

Apple supported carriers waived the charges, like mine I don't get any charges using iMessage.

Some carrier nickel & dime their customers with cheap plan but charges any extras.

Have a chat with your carrier and ask, they can tell you why.

You need to contact your carrier and let them know. Also try switching off imessage. Possibly restart phone/restore phone.

Sorry, I am also in Australia and I iMessage to lots to foreign countries in Asia, Europe and U.S.

FYI, Apple do not charge International SMS, all charges are from you telco.

No, it is always that way, maybe you should talk to your provider and ask why.

Sorry I have no idea why that number is used, where are you from?

Make sure that you’re connected to a cellular data or Wi-Fi network. If you're using an iPhone, you need SMS messaging to activate your phone number with iMessage and FaceTime. Depending on your carrier, you might be charged for this SMS.

From: If you get an error when trying to activate iMessage or FaceTime - Apple Support

No.

iMessage uses international text to Apple server to verify you.

iPhone supported carriers waived the charges. Talk to them or switch iMessage off.