Does Martialnote see or keep my credit card?

No. Payment takes place on Stripe's secure page, which receives and keeps the card and billing address. Martialnote never sees the card number. Martialnote only keeps Stripe identifiers (customer, subscription), amounts, dates and the subscription status, to know whether the school has paid. Support therefore can neither read nor change a card: the owner changes it in Manage my subscription.