@amiramiriOS especially for the iPhone 6 (last iOS is version 12) should not need to fiddle with the APN settings (since APN settings are automatically done via Carrier profiles).
I would suggest swapping your SIM card into another working phone to verify whether it is Public Mobile's issue or your phone's issue and go from there. Unfortunately Public Mobile doesn't haven't any stores or technical support it is up to the user to figure out what went wrong.
@amiramir FYI: You have posted to an old thread. In future you will have more assurance of help by creating your own topic on the forum (which I have done for you today), or, if appropriate, submitting a ticket to the moderators.
@amiramir Login to your account and look under Data & add-ons. If you do not see data listed, you have used it all.
If above suggestions don’t help,
Other things to try
Toggle airplane mode on, wait a few minutes and then off.
Lost/stolen phone trick. login into your account. Report your phone lost. Logout and wait a few minutes and login to report your phone found.