Who fitted them?
They should have fitted the Pro kit specifically for your car, for your car it should offer a 30mm drop which makes it the same as the petrol GTi.
The part is very different though, your car needs a spring to handle 1130kg load front and 1010kg rear and the GTi Petrol only needs to handle 1040kg front and 930kg rear. Part numbers are different and so are the springs, well worth checking.
Sounds to me like you've got petrol car springs and that would explain you're problem, my set up with Sportlines and Pro Dampers gives some bounce at around 100mph but it's a firm and positive form which corrects instantly and doesn't ever ground out and the car always remains really planted.
Just not as comfortable at speed as the original set-up but you will forgive that when you meet a corner. It's incredible for the price.
You'd have to go to a really well set up KW3 if you want a seriously good set-up and the dosh goes up too.
Go to Eibach and check what you have on your car and take it from there
