please visit https://eservices.cic.gc.ca/epay/faq.do
found the below note.
If you want a refund of your receipt and pay back the exact amount, you must send a refund request with the copy of the receipt by email IPRMS-SIGPR@CIC.GC.CA or by fax at 819-953-1377.
The request must include your name, current address, receipt number, the date of the transaction, amount and reason for the refund. If you do not have the receipt number, we will need the first two and the last four digits of the credit card used and its expiration date. You will also have to make another payment for the correct amount.