I also experienced your same issue when I first signed up - in my case my number was still in the process of porting from Freedom Mobile at the time - to complete this process may take up to 24 hours in some cases, even if you may be able to use data / text already this is normal.
I would also make sure you've finished setting up your Public Mobile account online and activated your e-mail (not here on the community but the account page).
If this is already complete then you should take your SIM card out of your phone, power off for a few seconds then put it back in and boot up.
Let us know how it goes.
Best of luck,