Require my sister to repay the money. The younger brother can first collect relevant evidence to prove that the credit card debt was used by the older sister, and require the older sister to repay the money. If the younger brother does not repay the money, the younger brother can file a lawsuit in the People's Court. A credit card, also called a credit card, is a credit certificate issued by a commercial bank or credit card company to consumers with qualified credit. It takes the form of a card with the name of the issuing bank, validity period, number, cardholder name and other contents printed on the front, and a magnetic stripe and signature strip on the back. Consumers holding credit cards can shop or consume at specially appointed commercial service departments, and then the bank will make settlements with merchants and cardholders. Cardholders can overdraft within the prescribed limit.