It so happened that you lost the phone. Or you stole it, God forbid. Just buy the new issue of inconvenient and dangerous: first, because it will have to restore the phone book (well, if she was somewhere recorded copy, for example, in a conventional written form) and to inform all friends, neighbors, and colleagues your new contact number, and second, because the old number should at least block to avoid unpleasant consequences, because the number is owned by you and who, where and how much will now with a call, you don't know.
To solve this problem comprehensively and effectively include recovery rooms.
With them you will need to take your passport.

Need to know the address of one of the offices or points your mobile operator as soon as possible to go to exclude the possibility that the new illegal owner will have time to do something with your room. You come to the office and say that you want to restore the room. You give a special form, specify your personal data (just for this passport was needed), then you will need to specify the reason for requesting a new SIM card and restore the number (loss or theft), then if all data is correct, the office staff will contact the people responsible for such activities and will give you a new SIM card.
Congratulations, your number is restored and you can continue to use it!
Of course, all the above works fine for hotel rooms, bought from official representatives of mobile operators with the necessary documentation, not in the market around the corner. We strongly recommend you always use the first way, and the problems with recovery rooms will not.
Good luck!