You can find all invoices associated with your account in the Epic Billing section.
Go to this site: https://www.epicshops.com/account/
Click on the Manage your billing account button and put in the email address you've used to sign up. Hit the Continue button.
Enter the One Time Password sent to your email and hit the Login button.
Once logged in, go to Billing History.
You can also hit the Download button if you wish to save a copy of your invoice.