1994 Nissan Micra Unable to open fuel lid

I have a 1994 Nissan Micra which has a lever by the driver's seat, to pull up for boot release and push down for release of the fuel cap door - normally you can feel some resistance when using the lever but now when I push down there is no resistance and the fuel cap lid is not opening, and can't be prized open, ie. I can't put any petrol in my car! Has a mechanism broken and will this be expensive to fix as I am selling/scrapping this car soon but need some petrol in it first!