Hi ihtayk,
Welcome to the Apple Support Communities!
It sounds like you may be seeing your device in Lost Mode. If you didn’t activate this mode and do not recognize the number, try logging into your iCloud account on the iCloud website and turning off Lost Mode.
iCloud: Use Lost Mode
You can turn off Lost Mode by entering the passcode on the device, or by following the steps below. You can also follow the steps below to change the contact information displayed on your lost device.
If your credit and debit cards for Apple Pay were suspended because you put your iPhone 6 or iPhone 6 Plus in Lost Mode, when you turn off Lost Mode and sign back in to iCloud, you can resume using your cards.
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Go to Find My iPhone on iCloud.com.
If you don’t see Find My iPhone on iCloud.com, your account just has access to iCloud web-only features. To gain access to other iCloud features, set up iCloud on your iOS device or Mac.
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Click All Devices, then select the device that’s in Lost Mode.
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Click Lost Mode, then change the information or click Stop Lost Mode.
If you are successful turning off Lost Mode, I would next suggest changing your iCloud Apple ID password. The next attached article below has information on how to change that password as well as some other great information I would suggest you read over.
If you think your Apple ID has been compromised - Apple Support
Best regards