1) The PUK code is a number unique to your Prepaid SIM/ Postpaid SIM card. It is used to prevent unauthorized use of your account, and keep your SIM details safe.
2) You can dial 199(toll free IVR) from another Vi number to navigate the menu and retrieve your PUK code to unblock your SIM.In case you are calling from a non Vi number, dial 10 digit circle long code, click here to know circle long code
3) In case you have lost your SIM & wish to block it click here