It's easy to get your receipts. Just go to the billing section in your org settings. To get access to past invoices & receipts, click on "Manage Subscription" which will take you to your Stripe billing portal.
Scroll down to the "invoice history" section and click on the invoice date to open up the invoice. Then just click "Download receipt" to get the receipt.
To ensure that you receive your receipts via email going forward, in the billing section of your org settings, scroll down to "Email Receipt Preferences" and turn it on.