When I had problems last year with the Wizzair site purchasing with any U.S. issued credit card (including Cap1), I found an Australian travel site that sold Wizzair tickets without any surcharge --- http://www.bestflights.com.au/

The immediate email acknowledgement that I received came from Wizzair, not Best Flights, and I was then able to add luggage fees on the Wizzair site using the same credit card that had been repeatedly rejected previously.

Incidentally, the Wizzair flights were outstanding --- on brand-new planes, complimentary juices and coffee, easy check-ins both ways (generally unheard of on LCCs).^ I have no idea whatsoever why they put up the credit card barrier, but with the Best Flights workaround everything worked out perfectly. I don't know whether the workaround is still working, but it might be worth giving it a try.