Little kid bothers me to often?

There's this little girl, she is very immature for her age. She is 8 but acts like a 6 year old. She obsessed with my little pony and she can't read, write, or spell. I don't know why. She is very slow.
Anyway her mom started to let her use the phone. So she starts calling me. She doesn't have really any friends. (BTW I'm her babysitter) so she calls me.
She calls me about 5 times every other day. And she leaves messages but I don't listen to them.
I started playing roblox, minecraft, and other games she likes. So when I do pick up she wants me to play with her. My limit to calling her is 30-45 mins. Then I just say I have to go because of Dinner. Have to go somewhere. Ect.
But when I say that she gets really ticked off like "Well if you wanna talk to me you're gonna have to do it now because for the next week I'm super busy!" I just say I will call her back later bye bye. And then she calls again the next day.
So I call her back cause I say I would, and so I stopped saying I'm gonna call you back and she just asks "Call me back?" I say "We will see." Then I say bye.
Well she messages me on roblox saying I ditched her spelling it "U dich me" I just reply back "Wut?"
WTF IS SHE TALKING ABOUT?!
I have put up with her for the longest time and I don't know should I go to her mom and ask her to limit her daughter or what?
It's getting on my nerves. She needs friends!

It sounds like she is an only child. I have one of those and they are usually starved for attention. My daughter has always had problems keeping friends because she is so desperate for friends that she tries to take over their lives. You should definitely talk with the mother about this, as it sounds like her daughter needs to learn boundaries. The sooner she learns them, the better. She needs to understand that you are her babysitter, not her peer. Only children often have a difficult time understanding social relationships because they don't have siblings who tell them when they are being inappropriate and annoying.