I don't remember the whole spell but theres an old voodoo spell calling for a cows tongue. I can't remember it exactly [and I've heard of one version where you cook and eat it and another where you put it in the freezer then throw it in a moving river] if memory serves you write the peoples names on pieces of paper, then place them in slits you cut into the cows tongue and seal them with needles. Ask in the voodoo section, someone will know the spell.
You could also try poppets and sewing their mouths shut as a symbolic measure of making these people stop talking about you. Ignoring them, while difficult, is one of the better routes. Curses come with negative energy, and from my experience the majority of people who gossip give up if you don't respond.