I'm wouldn't be 100% sure, but if the blower (at all speeds) is working but only through the windscreen vents then this would obviously inidcate that the interior fan is fine.
I would check for either a blockage in the system which could be simple or difficult depending where the blockage is. IT may be a case of removing the centre interior vents/ un clipping and checking, or from under the bonnet remove the black material cover to the right rear of the engine bay (the big one) and inspect the fan/flumes closer.
Other than this if it will not blow through the interior vents then the controller may be damaged which would involve removing the dashboard cover and inspecting further the control levers etc.
Sorry to be vague, but this is all I can say atm.