Baby_sham, I would be hurt and upset by all this, as you seem to be.
You really need to sit down and talk to your Mum and Dad, if you can't do that, or it doesn't resolve anything , then you need to stop being so available all the time for your Mum.
I don't mean cut her off completely, she is your Mum and you obviously love her, but don't be available all the time and learn to say no,
No sorry, I'm busy at the moment, but I can do it for you later in the week,
Perhaps you could do a babysitting swap with a friend,
Perhaps they would be more reliable.
They say ...you can choose your friends but you can't choose your family.
Good luck. X