I just started getting the same error today too with my J7. Been having the SIM card removed error from time to time over a year but now getting the locked error. Hard resetting isn't fixing it or removing it and putting it back in.
Hello, Luridan. Thank you for reaching out to us here. Sorry to hear that you’ve been experiencing this issue. Let's get this thing figured out.
Try to power off the phone, remove SIM Card, and gently wipe it off with a soft cloth. Reinsert the SIM card and turn the phone back on. Then, test the service to see if it works.
If the problem still persists, send us a private message with your phone number, pin code and address so we can take a closer look.