In a very similar situation, I called Expedia and they sent me an email confirming that my flight was cancelled, the airline only offers credits not refunds, and that I refuse the credit option. This email I then used with my bank for the credit card chargeback.
My bank took on the chargeback request, but said that it will take up to 30 days for a temporary credit to be posted to my account, and then if the merchant challenges the chargeback within 90 days, the temporary credit may disappear again.
In the 7 days since my chargeback, neither of the two has happened.