Are you able to plug a headphone cable in that has nothing on the other end. ie. no electrical connections for your phone to judge what is on the other end of the cable. I have some Sennheiser headphones that I can disconnect the cable from, when I plug just the cable in it still displays as headphones.
Also try plugging in the tv cable you got with the phone without it being pluged in to a tv, when I do this the phone cannot tell what has been plugged in.
I am thinking your problem maybe that somethnig in the headphone socket has got bent and it then incorrectly reports back as a tv cable.