I talked to my credit card CS yesterday (amex) regarding a Swiss booking and they mentioned that they consider a voucher a refund.

This means that, at least with amex nl, getting a voucher instead of cash is accepted and not cause for a chargeback to be approved.

I do agree that with the typical rules you should be able to get a cash refund. But things are not typical. If airlines have to provide refunds for every canceled ticket even the strongest ones will fold and go bankrupt.

I'd advise on taking the voucher and be happy that you got something back. After all it's not your fault all of this is happening.. But it's not the airlines fault either. Everybody will have to bear some of the costs.