It sounds like the gate for the shift lever is toast. Does the little lever on the front edge of the gear knob still work?
If you are feeling brave, you can pull up the gaitor base trim - put the shift lever into N, then using two fingers on BOTH hands, gently 'hook' each finger under each corner of the gaitor (you'll need to push the gaitor down) to get under the lip of the hard plastic trim - then just evenly pull up. The base trim of the gaitor should just pop up, and you can then check the white nylon gear lever 'gate' for any obvious brakages.
HTH