The buyer is able to escalate the dispute 3 days after you openned the dispute.
To escalate the dispute, the buyer needs to sign in and click on "My Orders"on the home page (tab is in the uppermost tool bar). This will bring the buyer to all orders he or she has made on AliExpress. On the right-hand side of the order in question will be several options for the buyer. One is "Escalate dispute", Click on the button.