Here is an explanation by one of the Oracles, Luddite.
SIM network PIN blocked. Enter SIM network PUK." is asking for the phone’s (often Samsung) “master code" after entering the wrong code too many times. Samsung and/or your previous carrier can give you this.
"SIM network unlock PIN" is asking for your previous carrier's unlock code - just contact them with your IMEI and they'll give it to you. If you enter this incorrectly too many times, you'll get the error message above.
“PIN unlock key (PUK)” is a SIM-specific code used to prevent unauthorised use of a SIM card.
The PIN (Personal Identification Number) enables secure access to the SIM card and network. It is provided with your SIM card.
If the PIN code is entered incorrectly 3 times, the phone is locked (except for emergency calls) and requires a PUK (Personal Unlock Key) to reactivate it.
Once the PUK is recovered and validated, you will be asked to choose a new PIN.
Only Public Mobile's moderators can give you this type of code, which the device manufacturer cannot. Public Mobile's moderators can be contacted by submitting a ticket at: https://publicmobile.ca.ada.support/chat/
Caution! If the PUK is entered incorrectly ten times in a row, the SIM card becomes unusable
