Cancel a purchase

Hi! I guess you mean to get back money?

You can go there:

https://reportaproblem.apple.com/

Then: What can we help you with? Under that choose > request a refund! And then follow the next directions!

Read more on: Request a refund for apps or content that you bought from Apple - Apple Support

What kind of purchase? You need to explain clearly what you are referring to.

I want to cancel a purchase about Grammarly.