Texting

An iPhone cannot send a text message from the iPhone without human intervention.

This means that either someone had physical access to your iPhone or another Apple device that allows SMS forwarding to send that message, or your SIM card/carrier account has been compromised.

Contact your carrier.

If other people have access to your iPhone or other Apple device, change the device passcode and never share it with others.

Change your Passcode -> Use a passcode with your iPhone, iPad, or iPod touch - Apple Support

Change your Apple ID password -> Change your Apple ID password - Apple Support (IE)

• Create a strong password for your Apple ID, It is best if your password consists of eight or more characters and include upper and lowercase letters, and at least one number. You can also add extra characters and punctuation marks to make your password even stronger. 
• Never provide your password, passcode, security questions, verification codes, recovery key or any other account security details to anyone else. Apple will never ask you for this information.

Then see this Apple article: What to do after you change your Apple ID or password

What to do after you change your Apple ID or password - Apple Support

(if you haven't already done this) Two-factor authentication for Apple ID -> Two-factor authentication for Apple ID - Apple Support

To keep your Apple ID account secure, see the following Apple articles: 

If you think your Apple ID has been compromised

If you think your Apple ID has been compromised - Apple Support

See who has access to your device or accounts

See who has access to your iPhone or iPad – Apple Support (UK)

Delete suspicious content from your devices

Delete suspicious content from your devices – Apple Support (UK)

Check your Apple ID device list to see where you're signed in

Check your Apple ID device list to find where you're signed in - Apple Support

• if you see devices that don't belong to you, delete from your account.

Personal Safety User Guide

Personal Safety User Guide – Apple Support (UK)

Manage and use your Apple ID

Manage and use your Apple ID – Apple Support (UK)

About the only texts that your phone will send on its own are iMessage and FaceTime control messages. These go to a number in the UK (country code 44). To see if that is what you are experiencing try turning them off and see if these messages stop.

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.

Hope this wil help you out -> https://www.shortcodes.org/uncategorized/474633-short-code

However, texts to 474633 continue albeit at a reduced rate.

See my post.

If you signed out, as I said, iMessage and FaceTime will not work.