How to make a Complaint to Costco Docklands Costco Docklands operates an easy to follow complaints procedure. The first step is to call the complaints line on (03) 8602 0300 (Mon – Fri: 10:00 am – 8:30 pm, Sat:9:30 am – 6:30 pm, Sun:10:00 am – 6:00 pm). They say the vast majority of complaints are