Can you get into neutral too? If so the linkage must be working partly, perhaps just about to break completely.
When I had a similar
problem on a Mk.2
Ibiza, it was one of the two levers on top of the gearbox, the one with a balance weight on it. It had actually broken. Fortunately there was a Seat dealer in town at the time and I was able to cycle to them, order the part and fit it myself - DIY fixing of these bits is easy.
The gearchange mechanism has two hefty Bowden cables between the gearstick and the gearbox, one for left-right movement of the stick and one for up-down, which is why everyone is saying it sounds like a linkage failure. Easy check is to look under the bonnet while someone else moves the gearstick through the shift pattern. The failure might be at the gearstick end.
Incidentally, the feel of the gearchange depends quite a lot on how stiff these cables are. The ones on my Toledo are very thick, with a massively stiff outer casing and a solid rod-like inner. The gearchange is very positive and waggle-free. On my old
Ibiza the cables were much thinner and the change was less pleasant, more "rubbery".