Just a quick update - I can no longer reset my password, so either they have actually deleted my account now (great!) or just changed the email address. Either way there is no use speculating now as my profile page is a 404 and there is no way to tell with certainty one way or the other whether my account has actually been removed (I suppose one could try to register the username "Lazer", but I am way too sick of this to go near their registration form again).

I filed an ICO report early this morning when the libel on their website stayed there overnight with no sign of changing hours after the cofounder's and Y Combinator president's replies; I simply didn't know what else to try and someone suggested looking into the ICO. So I guess it will just be in their hands now and I'll see what comes out of it, if anything. For now I think this is the end of the road in terms of getting the best possible outcome with a company like this. They are clearly not going to admit their mistake and they seem to still be in (seemingly really bad) damage control mode. I think any further interaction with them would just be a waste of time at this point.