What do I do?! TW

It has come to my attention that my MIL and SIL are conducting a smear campaign, spreading disgusting lies and rumors about me. No big deal bitches can be bitches, but recently I learned they're saying that I sexually assaulted my niece...What the actual FUCK. I was molested as a child and shared this with my SIL when things were seemingly good and I thought I could trust her. Turns out she is using my past trauma as a weapon to slander my character. This is nuts. What do I do, how do I clear my name of this atrocity. I'm baffled.