Check your payment history in your self service account. That might provide more useful information. Exact $5 charge is unusual since Public mobile will charge taxes on top of anything customer purchases.
If you're unaware of where the charge came from I suggest contacting customer support to clear things up. To contact support you can submit a ticket through the chatbot by pressing the chat bubble in the bottom corner and typing in "submit a ticket" and selecting "Contact Us". If that doesn't work you can message support directly from here: https://productioncommunity.publicmobile.ca/t5/notes/composepage/note-to-user-id/22437
