Why is my phone silenced when locked?

My phone does not ring when locked. I have checked the "Do Not Disturb" (it's off), the silent mode button is not active and works perfectly, the speaker works (I've tried changing my ringtone), and I'm allowing calls from everyone. This began when I got a popup message after several calls in a row from a spam caller with a note from my phone saying "you seem to be getting a lot of calls - would you like to silence them?" I replied "yes". Now I can't turn that option off. Help. If my phone doesn't ring I cannot do my job.