Long story but needed advice

Gonna use fake names😁

So brad and I were together for about 3-4 months and my mum and dad loved him, he was my first proper relationship , then his best friend Justin did everything with us went everywhere with us and it was us three , then Justin took a liking of me but it was kinda weird cause we were so close I could like cuddle with him and we thought nothing of it , but he liked me and he came over to mine and we cuddled up to me and played with my hair and it was a good day , then I got told that it looked more than friends from my mum so I told brad

He got shitty and we broke up

Then he told my mum horrible things about Justin and now my parents hate Justin

Justin and I are now dating and have been for nearly 3 months , I’ve seen him 2 times in that 3 months (one including my formal) ... I don’t know what to do , I’ve already tried telling them that it isn’t true (because it isn’t) but they refuse to let me see him ... it’s hurting our relationship ...