@indira
In general, since PM is prepaid, there is no refunds.
You will need to contact customer service agent. They are usually understanding of this issue.
You will need to contact customer service agent (CSA):
https://www.publicmobile.ca/en/on/chatbot. Type: wrong add on. Follow the prompts to submit ticket.
CSA may ask a few questions to verify account ownership and then should be able to help you. Response times can take a few hours. Check your private message inbox (envelope in upper right corner of website).