What should I do if a paper makes false claims about my work?
That is what the editor or technical chair of the venue is for: to act as an independent moderator. Contact them, clearly and briefly explain the situation and indicate that you previously contacted the authors before publication but received no reply. 

With overzealous spam filters, there is always a chance a reply came but was blocked. Start a constructive dialog so that the correct facts can be brought out in the correct publication (maybe yours will be revised to specify clear limits of applicability). It's a slow process to resolve such things, but it is certainly doable.