I need to cancel the last transaction!

Purchases are considered final but you could try the 'report a problem' page to contact iTunes Support and see if they will refund or credit you as a one-off : http://reportaproblem.apple.com

Or you can try contacting iTunes Support via : https://support.apple.com/contact or https://www.apple.com/emea/support/itunes/contact.html

Read my previous reply, you will have to try contacting iTunes Support and see what they say - we are fellow users, these are user forums, nobody on here can potentially refund you.