@OP:
Are you honestly blaming Duty Finder for this ? Because obviously, if you had to create a party from your server, things like that would NEVER happen, right ?...

I admit that what has been said in that dungeon is not very nice. In fact, as others pointed, you can use the ''Report For Harrassment'' feature in the Support Desk. I mean, it's a MMORPG, you will totally meet people like that now and then. Either you just ignore them, flame them, or report them.

Now, Duty Finder is just a great tool helping everyone. Just keep doing your job, keep practicing as a tank, you'll become better one day. And ignore those stupid people.