Thanks for the feedback, I had no idea that using a player name was an issue, so I apologise for that, although it is kind of ironic when reporting a griefer!
There is no clear way of reporting in game (unless you areferring to the option to "press charges" or whatever it is - there is never any feedback on it, so whilst I use it, I cannot report any success from doing so). I once accidentally shot someone who attacked my target and similarly had no way to apologise as there is no in-game chat.
With regard to reporting to R*, I should think they are so busy squashing the myriad and huge bugs to bother . . . the feedback I have got from that is next to valueless and gave the appearance that the issues I raised had not even been read, which is disappointing.
I do have a list of those who have acted unreasonably, so if anyone can point me in the right direction, I will happily hold them to account.