Well, the cancellation fee is $25 one way, plus tax. If you rebooked over the phone, you'll have to pay $3 more one way as web savings is not available.
Assuming that your ticket is a roundtrip, just the change fee is $53, plus you'll have to pay for additional $6 for phone fare. Hence, you won't get anything in return. The only time I do call westjet to cancel and rebook is when the one way fare drops more than $35, then it's worth it.