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Call your carrier. Log into your account on your carrier's website. Change your passwords.

Article:
If you don't have access to the internet, you can call your carrier's Customer Service line and have a representative deactivate the line for you. You will need to be able to identify yourself as the account holder. You may be able to deactivate the phone using an automated menu system. If you have multiple phone lines on the same account, you will need to specify which line needs to be deactivated.  Verizon - 1 (800) 922-0204 AT&T - 1 (800) 331-0500 Sprint - 1 (888) 211-4727 T-Mobile - 1 (877) 453-1304 Cricket - 1 (800) 274-2538 Vodafone UK - 0333 304 0191 You may need to provide the IMEI number for your missing device. If you can't call in your lost or stolen phone, you can use the carrier's website. Nearly all major carriers allow you to report your phone lost or stolen from your user page on their website. You will need to sign up for an account if you don't have one already, which usually involves confirming your phone number and personal information.  Find the "Suspend Service" or similar option. You will be guided through the process of suspending your service. You may need to provide the IMEI number for your missing device. If your iPhone or Android phone was lost or stolen, there's a good chance that it was tied to an account. As soon as you realize that your phone has been lost or stolen, change your Apple ID or Google password.