Mobile PUK codes - how do I find my PUK code?
If you have a PIN number on your SIM card as an extra security measure, you'll need to type the PIN number in each time you turn on your phone. If you do this wrong 3 times, the SIM card will be locked and you will be unable to use the phone. In this situation, you will need your PUK code to unlock the SIM.
WHAT IS A PUK CODE?
These codes have been around quite a long time actually and PUK stands for 'PIN Unlock Key'. It's a unique code that is linked to your specific SIM card and is usually 8 digits long. Some phones may ask for a PUC code instead. This stands for 'PIN Unlock Code' and is exactly the same thing as a PUK Code.
Mobile PUK codes - how do I find my PUK code?
If you have a PIN number on your SIM card as an extra security measure, you'll need to type the PIN number in each time you turn on your phone. If you do this wrong 3 times, the SIM card will be locked and you will be unable to use the phone. In this situation, you will need your PUK code to unlock the SIM.
WHAT IS A PUK CODE?
These codes have been around quite a long time actually and PUK stands for 'PIN Unlock Key'. It's a unique code that is linked to your specific SIM card and is usually 8 digits long. Some phones may ask for a PUC code instead. This stands for 'PIN Unlock Code' and is exactly the same thing as a PUK Code.
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WHERE DO I FIND MY PUK CODE?
The PUK code is unique to your SIM card, so you can only get this from your mobile network. Sometimes they will give you this when you first get the SIM card, but not all networks do this. If you cannot find it, give your mobile network a call and they will be able to give you the PUK code after you have answered some security questions.
To make things a bit easier for you, here are the contact details for the major networks:
Asda Mobile: http://www.asdamobile.com/contact.html
EE: http://explore.ee.co.uk/contact-us
Giff Gaff: http://giffgaff.com/boiler-plate/contact
Lyca Mobile: http://www.lycamobile.co.uk/en/contactus
02: http://www.o2.co.uk/contactus
Orange: http://explore.ee.co.uk/contact-us
T-Mobile: http://explore.ee.co.uk/contact-us
Talk Talk: http://www.talktalk.co.uk/contactus
Talkmobile: http://www.talkmobile.co.uk/help-and-advice/contact-us
Tesco Mobile: http://www.tescomobile.com/contact-us
Three: http://www.three.co.uk/Contact_us
Virgin: http://www.virginmedia.com
Vodafone: http://help.vodafone.co.uk
WHAT DO I DO WITH THE PUK CODE?
Once you have got the PUK code from your network, you will need to enter it into your phone. A notification will usually pop up, prompting you to enter the PUK code as soon as you turn your mobile on, so just follow the instructions onscreen to proceed.
As soon as your phone is unlocked, you may be asked to enter a new SIM PIN number, but this can be turned off in the settings menu of the phone once it's fully unlocked.
WARNING!
Do not try and guess your PUK code. If you enter it wrong 10 times, the SIM card will be permanently locked and you will need to get a new one from your network provider. There may be a charge for a new SIM card and you might be stuck without your phone for a couple of days while they send it out.

reference:
How to Unlock the PUK Code on Mobile Phone If Locked

how to video for Telstra but the bottom line is that you click on the link above for your phone service and follow the directions.

While unlocking is quite a long process, you can opt for professional unlocking service. I had recently unlocked my EE Phone. You can do it for free but the process takes a bit more time than usual.

So my advice will be to go for professional unlocking only. Refer this guide for more details
https://xtrium.com/can-i-unlock-ee-phone-free/

This site may help you. It describes a similar problem.

How to Unlock the PUK Code on Mobile Phone If Locked