YitAng
The most probable explanation why your CC doesn’t work is the not yet activated 3D-Secure feature, as already mentioned above: It’s a kind of multi-factor authentication anti-fraud mechanism, which is standard nowadays with European bank cards, and which is enforced by many webshops such as sbb.ch.
You can’t change this fact, so the mail or phone contact you’d need is your CC issuer or bank.
Otherwise, simply buy all your tickets on-site e.g. after arrival at the SBB airport travel center. Any regular tickets are always available in unlimited numbers and the prices won’t change (excepted for limited saver offers).