pay my entire phone balance in full

Unfortunately, there is no way to get a refund for your monthly bill. If you paid over the outstanding balance, it will show up as a credit on your next bill.

Actually, I meant to pay for the phone in installments, but I accidentally clicked on the option to pay the total amount upfront. Is there really nothing that can be done? I don't have that kind of money right now.

Thank you for clarifying. In that case, you will need to schedule a callback through Koodo Assist to speak with a rep. They should direct you to the appropriate department for the reversal of the charge. https://Koo.do/Chat