I’m really sorry you are experiencing all of this uncertainty within your friendship group, especially while we are in lockdown and the friends you thought you could turn to have been letting you down as well. This sounds like a really stressful time for you and I totally understand why you are confused on how to approach the situation.
When I was at school, I was also in a big friendship group, which was quite toxic and at times I wondered myself why we even hung out as there was a lot of arguments and cliques within this big group. But, when I went off to sixth form, I decided to come out of contact with people I didn’t really see adding value to my life and it was probably the best thing I ever did. By value I mean, friendships should bring something positive to your life and you should be bringing something positive to theirs too, it’s a two-way street. So, if you feel like you are in a friendship which isn’t valuing your life and is more pain then joy, then I think you should always let it go.
Now I know it’s really hard for you because you still have another year left at sixth form, but from the sounds of their behaviour, they aren’t your friends and they aren’t treating you how a friend should. Joining new friendship groups at sixth form can be tricky but remember it’s not impossible! Get talking to others in your classes, make bonds with other people and I’m sure you’ll find someone you get along with in no time. Also, forget anything about popularity (which I know is always big in sixth from), but I can assure you once you leave, popularity means nothing. Join groups outside of sixth form, where you could find some more like-minded people, who share the same interests etc as you. If you have a part time job, try and get to know the people you work with and form an outside of work friendship.
I don’t know what your plans are after sixth form, whether it’s university, travelling or going into full time work. But one thing I do know, is this won’t last forever. You will find a group of people that you click with and that are true friends, who will be a value to your life and treat you how you deserve to be treated!
Never change who you are, and you should never feel like you have to stand up for yourself within a friendship group. Wishing you all the best with your A Levels and the future!