It sounds silly, but I'm been bullied at college.?

I know by college things like this shouldn't happen, but I'm been bullied by people in my class. I'm in a wheelchair due to spinal cord syrinx, and these people in my tutor group keep grabbing the handles on my chair when I go past to make me lurch into the wall and putting their feet infront of my wheels. They always stand up really close to me towering over me and like, leer. I was going down a ramp once and they ran past and knocked me over over the edge of it and out of my chair. I don't think they actually meant to do that, because they picked me up afterwards, but the point is they keep doing things like this to me. They are both really popular in my group and I don't want to 'grass' on them because that'll make making freinds even more hard. I just need someway to persuade them not to bother me and for me to stand up to them.