Hello and thank you for choosing JA. My name is ***** ***** I will be attempting to help answer your question.
First off, i do believe google music is a free application. What you would be charged for would be a subscription for the services, or from downloads.
Google Refund Policy is as such:
You can return or cancel a music order within 7 days of purchase (14 days for users in the European Union) if you haven't downloaded or streamed the content.
Once you download or stream any music you purchase, you can't cancel your order unless the music is defective (as described in the Google Play Terms of Service).
But here is a link you can use to get a refund.
If I have made an acceptable attempt at answering your question, please rate and come back again for any follow-ups.
Thank you, Alex