Usually, simple SIM cards of the Kyivstar mobile operator, bought in some kind of stall or store, can be replaced independently with a new SIM card, for example, you can buy another SIM card there and call the operator, say that the old card is lost, report the last few dialed and accepted numbers, then the operator will block the old SIM card and activate a new one but with the same number that was on the old one.
This method of replacing a SIM card is often used by fraudsters, who usually call from different numbers, then loom back to call them back and then report the same numbers to the operator.
To prevent fraudsters from using this method, if your phone number is important to you, for example, a bank card is attached to it, you must activate the “Lock the self-replacement of SIM” service or register a SIM card using a passport.
To activate the service “Lock the self-replacement of SIM”, you must go to the My Kyivstar website (account.kyivstar.ua) and activate it yourself in the list of services or contact the official Kyivstar store.
On beautiful phone numbers, for example, in which there are identical numbers, I noticed this service already activated.
Other mobile operators have a similar service, just called differently.