How can I stop an app from charging me?

Hello,

I mistakenly took an application that costs 10 euro , I deleted it, I made changes in my phone after I realized that for 4 months I was getting money from the card for this application and I thought I'd solved the situation but every month I am charged with 2 euro i don't know for what. How can I get my money back and how can I stop this situation? I find it incredible how you can be fooled so easy...

[Edited by Moderator]