Baby dad brother hates me!!!

He always lying on me to my baby father and his family saying I said Or did things THAT I HAVE NEVER DID OR SAID! Mind you I don’t ever ever talk to him, we talked in the beginning of my baby dad and I relationship but I cut him off because he kept messaging me trying to start conversation whenever my baby dad was at work so I cut him off because it was a bit odd. After that he started making lies about me. I haven’t talked to him in over a year and he’s started shit maybe 10 times since then.. but this time takes the cake, he made a Facebook post saying I told him recently that my baby daddy said his brother deserved to get killed because he was a duck (their brother was killed in a tragic shooting) but I NEVER SAID THAT! How could I ? It’s such a harsh thing to say! The other times I wasn’t worried about it but this time it pissed me off cause what was said is so harsh!! What can I do about him? I’m fed up! My baby dad and his brother are always fussing as to why he won’t leave me alone! He act like he’s jealous or hurt! I’ve never led this guy on in any way nor do I talk to him! What the hell is going on? Why is he treating me this way?