hello, I would like to refund my money which is purchased for dropbox. I didn’t know that I subscribed dropbox. I don’t wanna subscribe it. There were misunderstanding I think.

If you subscribed through the app itself see this-->View, change, or cancel your subscriptions - Apple Support

Otherwise, you need to contact dropbox support. See-->Get help with subscriptions not billed through Apple - Apple Support

I'm assuming you purchased this through iTunes rather than direct from Dropbox. Strictly speaking all purchases are final - after all, you can't very well return them: please see this page for information on requesting a refund:

https://support.apple.com/HT204084

However Apple have been known to be sympathetic in cases of error, so it's possible that they may allow you a refund as a one-off concession: however please be aware that they are under no obligation to do so: go to

https://www.apple.com/emea/support/itunes/contact.html

Alternatively go to the page suggested in the Help page linked to above:

https://reportaproblem.apple.com/?s=6

Cancel the subscription so you don't get billed again.

https://support.apple.com/en-us/HT202039

https://help.dropbox.com/billing/cancel-dropbox-plus