Yes, you can still file a complaint after a transaction on Alibaba is closed. Even if a transaction has been completed or closed, if there are any issues or disputes between the buyer or seller, users can still file a complaint through Alibaba's complaint channel. Alibaba will investigate the complaint and take appropriate measures to resolve the issue in accordance with relevant policies and regulations. Therefore, users can rest assured that there are still ways to complain and seek solutions after the transaction is closed.