You have to contact the original carrier to which the phone is locked to. It should be a free service.
Public mobile has not sold phones for quite a while. If it is a Public mobile locked phone, you would need to contact moderator.
I'll add that Public Mobile will unlock or provide an unlock code for phones that are locked to Telus and Koodo.
@Jesstwest to contact a moderator and explain your situation. Click on the green questionmark in the white circle at the bottom right of your screen. This connects to the autobot Simon. Type moderator and follow the prompts to get to one (CLICK on "Account specific question" and "No I want a human" and "Submit a ticket Click me!")
Once connected, you will be asked to log in again with your community user name and password. Please do, this allows you to continue and send your message.
Check your private message sent box (click on the envelope top right of your screen) to make sure the message was sent. Also keep an eye on the envelope, the mods answer will show up there. Once it does, you will be asked to verify your self service account, with your password and login. Doing so allows the process to continue.
If you need to, you can also enable email notification to receive a private message notification sent to your email. Go to your community account > my settings > PREFERENCES > Private Messenger > enable "Receive email notifications for new private messages" > Save