The key is to submit all of the supporting documentation with the chargeback request.
1. E-ticket receipt.
2. Cancellation notice.
3. Request for refund.
4. Denial of refund or a note that no response has been received.
The key date will be the date you were notified (which could be when you looked or called).
The easier you make it for the card issuer to process, the more likely you are to succeed and to succeed quickly.