So this was resolved. I went to another dealer and asked them to check the VIN. They confirmed it was a VTI build.
I went back to the original dealer with the information and they were very apologetic. They said the car had actually come in from another one of their franchises and they hadn't bothered doing any checks, as externally it is optioned up to look like an S. I had done a bit of research on the difference in the resale value between a VTI and the VTI-S and it equated to about $700 for my year model. I negotiated with them and ended up accepting an $800 refund. They were actually very good about it.
In the end I have a optioned up VTI for much the same price as a standard VTi so can't complain.
Just goes to show you have to check things though.
Thanks for your replies by the way. This looks like a good forum site.

Tim