Am I sinning by helping my father pay the satellite TV bill, knowing that I cannot control what is watched?

If the father and the household are watching forbidden things, then it is not permissible to assist them in that, based on the Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." There is no obedience to the father in disobedience to Allah. However, if the viewing is only of permissible and beneficial things, then you must obey your father and help him as much as you can.