If you search online forums or YouTube comments, you will often see claims of universal codes or "master passwords" that can unlock the SM-B312E instantly.

A completely different problem occurs when you insert a SIM from another carrier. Instead of a normal PIN screen, the Samsung SM-B312E might show:

If you can still access the dial pad (sometimes reachable via an "Emergency Call" button or if the phone asks for a code on a home screen), you can perform a Full EEPROM Reset