I can't find one either. It seems these days a number of companies have moved away from support e-mails because other channels are much easier for them to manage. (Twitter is the same way, for example.)
If you still need it, this is Nintendo's official support page on this issue: https://en-americas-support.nintendo.com/app/answers/detail/a_id/28987/kw/country/p/994/c/186
tl;dr, they'll probably send you back to the bank that gave you the card. It might be a problem with the bank, not with Nintendo.
Either way, here's Ninty's contact page. https://en-americas-support.nintendo.com/app/contact
The card is charged about 7 days before the game's release. If the old card on your account is still active, I'd assume it'll charge that one.
Like Armchair General said though, Nintendo's support would know best. Good luck.