how can i get it off?

i have a P reg citroen saxo and i cant get the immobiliser to go off a few years ago the rac cut the wires on it as i had a problem with my alarm then they cut the wires on the alarm i was able to use the car then i took it off the road for a couple of years then i started using it no problems then one day it wouldnt start i had it towed to a citroen garage and they said the immobiliser had some how reset itself and beause i cant remember the code it was going to cost me more than the cars worth to sort out can anyone help me thanks