It sounds to me like you have undone the WHOLE bottom pulley. I've never worked on a saxo so I don't know whether I am 100% correct but on some cars the bottom pulley is in two halves. One half is where cambelt would sit on and the other half is where the alternator belt would sit. It sounds like you have undone the bottom pulley including the cambelt part. If this is the case you MAY get away with just tightening back up but if It was my car I defo crank over by hand before starting up. Hope this helps mate. Also if the bottom pulley hasn't actually come away from the engine then you should be ok just to whip it back up. As above crank over by hand to be on safe side just incase the crank has moved.