change plan student

Good morning,
I ask for help if possible.
I tried to change students' plans: from photography to all the apps.
I read from instructions that I have to cancel my current plan and then buy a new plan.
I've done all.
Now my account tells me that I have the old plan canceled but I have no chance to change.
In addition I have to pay a penalty of 24 euros.
Can anyone help me?
Thank you
Nicole