how do i fix my citroen c5 which was up to door sill in a recent flood?

the electronics now have a mind of their own, windows open without warning, wipers start up , lights come on and go off etc at various times what can i do?
The dealer states it might pay for me to call the insurers but I have a £350 excess. I wonder if there is anything I can do, or what it would cost for a garage to repair. The car is a citroen C5 estate.