Bank of China sent me a text message saying that my card was in arrears and the card had not been used. As for the tuition fee, what are the consequences of not repaying it?

Check with Bank of China. If it is a credit card and there are annual fees, etc., pay it as soon as possible, otherwise it will affect your future loans and credit card applications. If it is an ordinary debit card, there should be no such thing as arrears. Moreover, if you are paying for your studies, there is no need to use a credit card. It is better to get a debit card.