I think too many failed attempts for adding the credit card. You need to open ticket with PM Support and have them to check it for you. They can unlock if it there is any kind of fraud lock
at : https://publicmobile.ca/chatbot. Follow this to get to ticket open screen quicker:
start by typing : Contact CS Agent
then Click "Contact Us"
then Click "Other"
finally Click "Click here to submit a ticket"
you will then direct to another page to open ticket.
After ticket is submitted, make sure to check your Community Inbox(top right corner envelope icon) periodically for response from PM's CS Agent
If you have problems submitting a ticket, you can also send a private message to the CS Agent (but this can take longer):