it could be the Gear Selector Lever Bushes need replacing, i could only find a panda diagram but apparently it only takes an hour to do and it's not a difficult job.
it may help. they are i think the same as the punto.

or it could be the linkage.
to check: take off the bottom gaiter (its plastic/leather effect) and it just lifts out if you bend the sides in gently (dependant if its SX and higher from a certain age they have the centre console and that is a little different). Have a look at the linkages and see if they are broken or damaged. Also the age of box, they're known for being a a pain, so it could be the synchrocones gone inside the gearbox.