Problem wth Cigarette lighter socket/Power Scocket

Hi, Hopefully somebody can help me. My 2007 Octavia has no power to the cigarette lighter socket which I use to run the sat nav. I have checked the fuse which is ok & tried a different adapter in the socket & it is still dead. It was going off intermittently to start with & it would come back on just by pushing the adapter back in the socket again. I read somewhere that there was 2 fuses for this but on the fuse map it only shows 1. Any ideas?