How to find out who is harrasing me from a Pinger number?

I doubt you can since it’s from a free service.

I doubt it too. Unless the app provides customer support and they keep track of all incoming calls, you may be out of luck. It’s a slight chance your cell phone carrier may have a record of this, not really sure, it’s a long shot but you could contact your cell provider. Have you tried searching for the number online?
Is there an option to block phone numbers within the app? If you can’t find out who’s been calling you, you might just have to block them so they can no longer call you or just delete the app altogether.

Block the number through your cell carrier.
Most carriers are able to block with an on-line request or web page ( must be logged on to your account with a password ).

OR

Go to your cell carrier’s local store and give a written request.

Do you have an android? block the number through an app problem solved.