Hey. First of all I want you to understand that the situation that you are in is not your fault. People, especially school aged teenagers can be vicious and nasty and school is like survival of the fittest, people don't think twice about using others as ladder rungs up the social pyramid.
I was bullied in a similar way to you through years 7, 8 and 9. As terrible as it is, the only way it got any better was when I cut certain people out of my life entirely (in your case, this would be the girl that started these rumours and any of your other friends who support her or tell you "It's just a joke, get over it."). Once I did this, I settled into a new friendship group with the rest of the "outcasts" in my year group (At lunch we sat with the unpopular people from every year group in the school. It was like our own little subculture!)
I got incredibly good at ignoring the taunts and little comments people would make in class to me. I deactivated my social media accounts and blocked people's numbers so that they couldn't access me outside of school. I also joined a scout group, which proved to me that I wasn't the issue. The kids at scouts were all happy to be my friends (10 years later and we all still talk!!) so the issue clearly didn't lie with me.
Once they see that they aren't getting a response or a rise out of you, I'm sure they will stop.
Do you have a learning mentor at school? It may be worth approaching them as they can help you with coping strategies etc and also advocate to you to teachers and heads of year, making it easier to get things sorted through those channels too.