How can I cansel the purchase?

Hello,

iTunes or App Store purchase: Request a refund for an App Store or iTunes Store purchase

Apple Online Store: Viewing & Changing Orders

You can try contacting iTunes Support. Either use the form or scroll to the bottom of the page in the 2nd link. Follow through the screens to get a chat or telephone option.  You may need to pick a problem that is slightly different than yours to get a chat option.  

iTunes Support

iTunes Support – world wide