Hello strange question perhaps, but how can I recover the serial number registered with Philips?

The reason for asking is that when you initially register a WACS product you are asked for the serial number. I sent a unit off for an out of warranty repair and I am certain that the unit returned is not mine as cosmetically it looks dirty and has some marks that were not previously there.

Accordingly I do not have a copy of my units serial number to compare with the returned unit and was hoping to obtain it from the Club Philips web site under my account bvut under the registered products it does not detail any serial numbers (I am sure it used to).