Racism

Is saying someone's name wrong on purpose despite knowing their real name racist?
(I'm ethnic)

It's definitely disrespectful, and probably frustrating. Try to remain calm and maybe you can confront them. They might think it's OK to anglicise your name (make it more English) and you can explain to them that it's not. But if they're doing it to make you angry then you would be right to report it.

If they are your friend remember they may just be pulling your leg. However, if it is not your friend it may be a sign they are being racist but hold this as the last possiblity.

They're not my friends, they're the school "popular girls" so that's how you know it's genuine and they always seems to treat me different from others which makes me feel like it's indirect racism.

ah, very sorry to hear. It definitely may be rooted in racism, regardless its wrong. They are probably just trying to make up for the eventuality that they peaked in high school. In terms of telling teachers its up to you, personally I wouldn't be able to do it either but if it worsens remember there is always people that can help you.

Not automatically connected with anything racial.

Immature jerks often like to bait reactions from normal people and within their friendship groups are often in the habit of giving each other idiotic or very vulgar nicknames.
Can frequently be a form of teasing or flirting amongst teenagers & tweenies.
There will also be a few cliques that view themselves as the elite ruling the school who will have a habit of deliberately mispronouncing names or getting ages & addresses wrong to show that the individual is not worth remembering much about.

While the classroom and playground school bullies will often try to insult or humiliate their targets where it is likely to hurt the most.
Acne, address, allergies, braces, clothes, grades, hair colour, height, money, name, parents, phone, religion, sexual history, weight.