I can tell you what I would do, but a lot of people think I'm mean and callous. I would tell them the next time they bring it up that "I have apologized, and offered help to rectify it, and I can't think of anything else to do to make things better so please stop bringing it up and accept my apology because like I've already said. I am honesty deeply sorry for what I did. And it has not and will not happen again." And from then on pointedly ignore any comments on the matter.