(depending on which model you have, if it originally had a motorised petrol cap lock.)
there is a servo motor unit fitted up in the top of the wheel arch. you need to remove the inner arch splash guard. the servo also passes into the inside of the wing panel. it is held on via a 16/18mm(i think) nut.
inner boot trim will also need checking to see if it needs to come off, (to assist in ease of access.)
both the filler cover and the servo need replacing. the servo probably has had the pin snapped off and the flap click-clamp is broken off.
(was thge petrol cap opened by force???)
you will need to get replacement parts off a scrap vehicle (its the cheapest option for repairing your car)
the filler unit will have to be removed, the tank might need to be lowered to allow the filler unit to be removed, as it fits under the filler cover and holds the cover in place to the body panel.
if you want cheap parts try here,
they probably have a similar model available to be stripped for parts and they do mail order.