This is Finley from the Social Care team at Shopify.
Thank you for reaching out. I'm sorry to hear you weren't able to close your store before the end of the free trial.
To ensure your store is closed and that you will no longer be charged, please take the following steps:
1) Log in to your Shopify Admin.
2) On the bottom left, click on Settings and then click on Plan and permissions.
3) From here, scroll down to Store Status and click Sell or Close Store.
4) Follow the prompts to complete the cancellation. You'll be able to select a reason for why you're closing your store from the drop-down menu and then click Close store.
5) As a final step, you can go to your store's URL and check to see that your Shopify store no longer appears.
All these steps are showed in our Help Doc.
For the refund request, please reply to the email I've sent you. From there, we can have a look at your account together to see if a refund may be an option.
All the best,