Unknown number in iMessage

Hi,

recently i noticed that when i try to turn on iMessage it shows up on a phone number i don't know so i can't set my own phone number. Tried to reset iCloud password to get the phone numbers disconnected, it didn't help. The number cannot be deleted from the account settings. The phone number displayed in iMessage does not belong to any of my friends, moreover, this number does not exist (after calling, I hear that the number does not exist). Does anyone know how to remove this number from iMessage and can help me with that?

[Image Edited by Moderator to Remove Personal Information]