The best thing to do is tell someone about the bullying. Go to a teacher or school counselor. I know this is probably what you really don't want to do but it is just going to keep going if you don't speak up. Speaking to someone does not make matters worse, it will help you trust me I know. I had been bullied a lot throughout school and I know what it feels like to have zero self esteem and to feel so low that you don't want to come to school any more.
You've tried ignoring it and speaking up to them, now it's time to do something about it. I've ignored bullying before and kept it quiet but it just went on and on until I was at my lowest. Speaking to someone about the bullying was the best thing I ever did. Please speak to someone about the bullying, don't let the bullies win and take the verbal abuse - you can be stronger than that and tell someone.