You can cancel a WestJet flight upto 2 hours before its departure. When you change booking within 24 hours of purchase, you are only subject to a change in fare, and no service fee is levied on you. Cancel the WestJet ticket within 24 hours to avoid a penalty fee.
https://community.abebooks.co.uk/s/question/0D58V00009LmSPWSA3/18775590182-qatar-airways-cancellation-policy-cancel-a-flight-on-qatar-airways