knocking from rear passanger side

[campusdan]

I had new 40mm springs fitted to my campus sport 2006 yesterday and i was chuffed to bits ! It felt great to drive home but as i came up the hill where i live there was a loud bang from the rear and now going over bumps etc its making a loud knoking noise ive been under the car jacked it up etc and the new springs look fine ! Any advice help etc would be appreciated