Activate you SIM with a new number.
After your new SIM is working, port your number from your Public Mobile account https://www.publicmobile.ca/en/qc/get-help/articles/change-your-phone-number
Don't ask Koodo to cancel your phone before your number is ported to Public Mobile. Your Koodo plan should be cancel with port request.
If your number is not ported after one day, ask Moderator_Team to help https://productioncommunity.publicmobile.ca/t5/notes/composepage/note-to-user-id/22437
Public Mobile Moderator Team: https://productioncommunity.publicmobile.ca/t5/Knowledge-Base/The-Public-Mobile-Moderator-Team/ta-p/...