How can I get my sister to hear me out?

My sister has 2 young children who I am very close to.Within 2 weeks of splitting with the kid's father,my sister met a new man and had him move in.He is on parole,came right from a drug rehab center,and things got worse.I started to notice his inappropriate behavior with the younger of the 2 kids.I talked to my sister about it but she said I was being paranoid.Showers,backrubs and other worrysome things continued between him and this child,and eventually I called child services.They were extremely concerned and have recently told my sister an investigation will be done.My sister has found out that it was I who made the report and has said I will never see her children again.I spend time with these kids everyday,we live next door to each other and I take care of them while my sister works.This is breaking my heart.I understand her feelings of betrayal but I felt it needed to be done.How can I explain & get her to listen when she'll have nothing to do with me?Was what I did wrong?