My sister slept with my ex and my family deny he's the father!!!??

I broke up with my boyfriend partially because he constantly flirted. My boyfriend and I have a 1-month-old baby, where he denies he's the father. At the time I conceived I only slept with my ex and I never slept since. When I was 3 months pregnant I accidentally walked in on my sister sleeping with my ex. I never knew my sister even had a boyfriend until I caught her. My family don't care. My family also deny he's the father. My ex gives my family money and my family tell me that I am jealous because he's rich and I want his money (I have a low income and can't support my son). My family called me a hoe and told me to leave them alone and to leave my sister and her boyfriend alone. My sister also told me to leave them alone and that I'm a disgrace to her relationship. My family also have money and won't help me support my baby. I tried filing for child support because he won't pay and refuses to take a paternity test. What do I do?