How do I deal with harassment as I am only a Temp Resident?

This couple that my husband befriended about 3 or 4 months ago, while I was still in the United States still, has gone crazy on us because they had the idea that we were going to be a polyamorous 4 way couple when I gained residency. My husband and I thought this was a giant joke and so we never made anything of it until I got my Temp Residency and they started trying to initiate their plan. Needless to say that my husband and I are not looking for a polyamorous relationship and we let them know this nicely, first...then, sternly...and finally, maybe a bit rudely. It was at this point that they started making crazy threats to me and my husband. To my husband it was things like physical harm and defamation. To me, it was things like deportation through vicious lies. Now, we are not worried as they do not know where we live and anything that they could lie about would be found to be very untrue pending an investigation. We just want to know how to get them to go away without any further bother.