Any chance your brother used the same wifi network or even device to access his Rollbit account, just like you did?
If he did, then they (Rollbit) believe that you are the same person. Most casinos prohibit multi-accounting, especially if one account was banned. Good luck convincing that he was your brother and you are you.

I also have a feeling that "tip" might have caused you some trouble. Again, maybe they think the tip sender and the receiver are the same person. We don't know for sure. Only you and Rollbit technical stuff know better.