Perhaps he means that he got a serial for v8 but not one for v9 to enable him to install that version.
I had the same thing. I was told that I could get a free upgrade to v9 but I was never given a serial number for v9. You'll need to contact Sony to make sure you meet the upgrade window (30 day) requirement and they'll help you obtain the correct serial number. Unfortunately, my purchase was at around 40 days and they wouldn't budge.
Was it in a box? If so, it should have included a paper with the serial number on it. If the box was opened prior to you purchasing it, the SN paper may have come out.
Did it ask you for the serial number when you installed VMS? What does the splash screen say?