How to block IMEI number

At a practical level in most countries you can't get IMEI blocked. Where IMEI block lists exist they are usually maintained by the individual cellular networks to lock out devices which are either stolen from customers, or more often contract devices which have overdue and delinquent payments. They are sometimes mutually shared with other networks in the same country, but very rarely outside the home country, and they almost never accept third party requests to block.

File a police report and contact your cellular provider