Hyde here from Shopify.
Before I can look into refund options for yourself, you will need to close your store. For security reasons, we ask that the store owner logs in to close the shop. We have instructions here on how to do that.
You would need to login, go to Settings > Plan and Permissions, and scroll all the way to the bottom - there is a section about closing your account. Click on "close my store" and follow the prompts then your account will be closed and the billing will stop.
I'm going to send you an email shortly. If you could reply to that from the email address you opened your account with, I can then look into the refund options for you!
I hope this all helps!
All the best, Hyde.