Please help me...How can I get a refund?

What app did you not use? Stock is not an app, it's a service. And there is no deduction without a subscription, so you did take a subscription, even if it was the test subscription. At the end of the test, it converts to a paid subscription that can be cancelled free of charge into the first 14 days of the paid subscription. After that, you have an annual subscription and if you cancel, early termination fees will apply. The early termination fees, however, are less than what you will have to pay if you continue the subscription and cancel at the end of the year. 

To cancel, go to https://account.adobe.com/plans, click manage plan, and cancel.

Ich you cannot cancel yourself, check with Aodobe customer service. Adobe customer care can be contacted by beginning a secure chat session at https://helpx.adobe.com/contact.html?rghtup=autoOpen. Pop-up blockers need to be disabled, you need to accept cookies! If the chat window fails to open, or is non-responsive, use a different device and/or browser to start the interaction.

For support via Twitter:
https://twitter.com/AdobeCare

(see also here: https://community.adobe.com/t5/creative-cloud-services/how-to-contact-adobe-support/td-p/11875703 or here
https://community.adobe.com/t5/account-payment-plan/how-to-contact-adobe-support/td-p/11843852)

Important: Adobe does NOT contact you unsolicited by e-mail or direct message. If you get contacted by direct message from a person, claiming to be an Adobe employee, look at that profile and check if they bear the “Adobe Employee” marking under their name. Adobe support does not use Skype to give you support.
If in doubt, ask the forum.