I use SoftLayer API SoftLayer_Billing_Item :: cancelItem (...) to cancel hourly virtual server billing item, then calls
https://api.softlayer.com/rest/v3/SoftLayer_Billing_Item/$billingItemId/getCancellationRequests?objectMask=mask[ticket]
to get all cancellation requests.
But this API methods returns empty value even I can find the cancellation ticket was created on customer portal.
Why this API method returns empty value ? It looks like a bug.
It looks an issue I recomend you to submmit a ticket in softlayer, in order they can look into that.