First off, check security of gearshift rod at the back underside of the gearbox, if it has come loose or moved, move back to wear witness marks say it was and tighten clamp.

I reckon your gears rods and linkages may have worn. These will need to be replaced, and i'd recommend to replace the whole set to prevent you having further problems with them.

I had the same problem on a '98 saxo a couple of years back. We are probably talking around the start of a three figure sum to get that problem sorted.