You need to spend some time today to get yourself organised and your plan of attack mapped out. Get prepared, have a plan and follow it. Also, know what you want the outcome to be (ie you want a full refund for the car and any money you have spent on it in
repairs and
maintenance).
Make sure you have the original advert, your receipt, and all the paperwork that confirms it advertised and sold as a turbo. Then in parallel with all the other stuff for tomorrow start to gather the info from Seat that confirms it as a non-turbo from new. As you said earlier that a
Seat dealer confirmed it was sold as a non-turbo from new, see if they would be prepared to put that in writing on headed paper for you.
All the car search agencies and insurance companies base the car details and model on the original log book which may have been listed wrong from new - they accept whatever the registering
dealer put down. I know this because my FR was originally listed as a Cupra and I could not insure it (before delivery and receiving the log book) as an FR when new, so I contacted DVLA and had it changed to an FR and new log book issued as a correction (I bought it new as an FR so its not a dodgy change!!). After that, I could insure it as an FR!
Either way, a car
dealer is classed as a professional in his/her field of expertise and would be expected to have spotted the mistake by trading standards etc. He would not have a leg to stand on in court and your engine number should match the log book, which obviously would not have been altered since you had it, so he couldn't claim you'd changed the engine or anything. Get this dispute put into the hands of trading standards tomorrow 1st thing and seek their advise as to how best to pursue your claim. I reckon they will first tell you to put the complaint in writing to him and sent registered post so you can prove delivery if it goes to court.
It'll be a pain but you can claim all costs from him when he loses the battle - which he will. Not sure of your "homeowner" status but a lot of home insurance covers legal advice and assistance etc so you might be able to do something there - even if you still live with parents.
If your car is financed, the finance company would also take an interest (although "personal loans" agencies/banks might not be so interested).
Lastly - does he advertise as being a member of a professional body or organisation of any sort ? Contact them too as they have a charter by which their members must operate. He will be in breach and they will also want to have a word with him and may
help you too.
Be warned though - if you've had the car for any length of time you might hit a bit of an issue as there is only so long they give you before they will say that you have legally accepted the goods "as is". Get that legal advice tomorrow mate so you know exactly where you stand.