Bottom line is if C/C asks the man to turn it off and he does not, 2nd step is for CC to advise the captain. It should be the captains responsibility to resolve the issue on the ground, in the worst case scenario return to the gate and eject the passenger. This is the only proper course of action. If anything happened as a result of the passenger operating a mobile phone (not at all ever likely), the Airline would be completely liable.
You would be a fool to take any action upon yourself other than persistent notification to the dizzy blond F/A who just wants to get home (or the hotel) as soon as possible. If you really wanted to be persistent you could threaten to report the C/C to the CAA and airline. If she had notified the captain and the flight continued, the airline and CAA would place the blame on the captain. If you really wanted to be persistent you could probably march down to your local CAA office and ask to complete a flight safety report or equivalent.