Skoda Octavia whining noise from transmission?

Has the retailer even checked the box oil level?

You sure it's transmission noise and not possibly tyre noise or something else ? Different brands of tyres can have a big say on handling and noise levels .Get dealership to have a technician road test car with you and point out exactly what you are complaining about .That way the complaint will be logged into the system and give you something to fall back on if needed further down the line .Ask to drive another same car to compare .Take to another dealership for testing if not getting anywhere .If it's the DSG trans the oil should be changed every 40,000 mls.If still not happy get on to the Technical services / Customer services at factory and complain .