Finally receiving refund for flight scheduled for 6/10/20. Note that they stopped selling tickets for this flight in April.
5/19 Received email to cancel through the website, which wouldn't work. Called four times before getting through. They fixed the website problem and told me to go back to the website to request a refund. Which I did.
5/28 Received email with voucher credit (which I didn't want) which said to call if I wanted full refund. I called and was told my credit card would be refunded within eight weeks.
6/5 Received email from Vueling that they'd processed my refund and I should see it on my Amex within a few days.