Should I report this to the police?

[RatedRKOMizfit]

There are a group of girls in my sixth form a year above my friends & I, & they're constantly trying new ways to trigger a reaction. I'm not going to go into detail about that because it'll be pretty long, but we've reported them to the head (quite a while ago) & nothing was done about it. One of the girls from this group has a younger sister in my year, & she encourages her to join in on hating us.

One of the girls had uploaded a picture she took of us (twice) & both times we found out we reported her to the head who made her write a written apology, but she then privatised her (twitter) account so we can no longer see if she does it again. One of my friends is suspicious that one of the girls was taking a picture of us recently because her camera was flashing in our direction.

We've also noticed them tweeting about us using code names for us and making ridiculous comments.

What I (we) don't understand is what we've actually done to them that makes us the target. We've decided that they probably see us as a threat because we're external students who keep "ourselves to ourselves", or in other words we mind our own business. Stupid, I know.

If the school doesn't do anything about it, then we'll end up being victimised for the entire duration of college, and ignoring it DOES NOT WORK.
We tried to let the events blow over, assuming that they'd stop if we ignore them and do nothing in terms of revenge (like I said, I am not going to mention ALL of the horrendous things they've done to us), but clearly that didn't work. They haven't stopped & our rivalry is getting to its worst - we're considering taking it into our own hands if the police wouldn't consider it such a serious matter.

So what would they say?

PS would the head kick us out of school if we complained to the police that they did nothing about it?