Credit cards without limit cannot be overdrawn. The reason why this happens is because your qualification was not reached when the bank approved it, so you only approved the card without a quota.

If you want to increase the quota, it is easy to deposit money in your card and spend it for six months in a row. Call the customer service of Bank of China and ask for an increase in the quota. At this time, the bank will review it again and give you a quota if it passes.