Getting a refund From Cancelled TAP Air Portugal flight due to COVID-19 [duplicate]

Our TAP Air Portugal flight From San Francisco to Barcelona, scheduled for Apr 28, 2020, was canceled by the airline. We called TAP Air Portugal and asked for a full refund to our credit card, which was the original form of payment. The airline representative confirmed that a refund to a credit card would be issued. However, a few days later we received "TAP Vouchers" from the airline, which expire in March 2021, and which were not what we asked for. We called the airline again and asked for a refund to a credit card once more, but we got a reply "Vouchers are how we handle flight cancellations due to COVID-19 policy". Any attempts to get more information led to the same phrase repeated again. We filed a complaint on TAP Air Portugal official website but still didn't get any reply from the airline.

We believe we have a right to get a refund according to EU Regulation (EC) No 261/2004, Article 8, which is confirmed by EU COVID-19 guidance.

Do you know what we can do next to get our money back to the credit card?