I just went through this issue myself so I wanted to write about my experience with it to add to what's already posted in the community and update/refresh things a little in terms of procedure as these things can change over time.
If something goes wrong with your PIN and you are suddenly locked out of your SIM and your phone services as a result of this (as I just experienced), then you`ll need to use your PUK
(Personal Unlocking Key or Pin Unlocking Key)
to unlock the SIM. Unless you've already obtained the PUK, you can request one by sending a PM to the moderators to ask for it. They`ll need to verify your identity through an online verification page and at the same time you will need to send them your SIM number (this is a 19 digit number printed on the SIM card itself). Once that's all done, they'lll send you a PUK (or two, I received two from the moderators so I suppose there may be two for each SIM card?). Now you're ready to go through the process to unlock the SIM and get your phone and your life back;) Here are the steps:
1)Restart the phone(turn off/ turn on the phone)
2)Input on the phone either PIN Unblocking Key 1-> XXXXXXXX or PIN Unblocking Key 2->XXXXXXXX and press OK.
3)Choose your new 4 digit numerical PIN.
4) Test your phone and see if you can make calls, send text messages and go on the internet using your mobile data.
Everything should work ok by then, and as they, "Bob's your Uncle!"
