OP, firstly, the only people I was critical of on this thread were those suggesting that you all meet up and have the catfish round for dinner etc.. All totally idiotic suggestions.
You did what you could in the circumstances.
As things have escalated to the degree they have I suggest that you A, cancel the sleepover, and tell your DD that you’ll be telling her best friend’s parents why, as BF also needs protecting.
B, search her room from top to bottom and remove all technology, tablets/phones/laptops and from now on technology is only used in a communal space.
C, remove her smartphone permanently and buy her a brick phone.
D, stop her allowance. She can’t be trusted not to use it to buy new tech.
E, speak to the police again regarding how this has escalated, and tell your DD that as she’s now involved with these people, she is culpable in the harassment of you and your DH.
The time for talking is over. There need to be consequences now, and they need to be serious consequences.