velux blind doesn't closing anymore(manaul rolling blind)?

I've had blind for velux windows,it was worked perfectly but now,i've got problem them blinds weren't close anymore,every time i pulled down it always rolled back to the top slowly and opened itself completely after.is anyone know how to fix this problem??
i rang the place where i've got them blinds installed.but their never cames out to fix them..and i would recommend not to get blind from this place(BRADY BLIND) in DROGHEDA, no service after sell.
and wanted it in their way,by not to listened to the customers...

bubble blue
June 2010