You can access your Billing page by going to Settings > Billing to see your plan, invoices and change payment details.
When you access billing you need to confirm your email address by including the confirmation code that you will receive by email.
If you don't receive the confirmation code in your email, these might be the issues and solutions:
You might not be using the correct email address to access Billing. You need to use the email address that is associated with the premium account. This is the email address that is used to sign up for the premium account. If you use a different email address, you won't receive the confirmation mail.
The email might have landed in your spam mailbox. Please check your spam mailbox to see if the email
It could take a few minutes before you receive the confirmation code. Please wait a moment and see if the confirmation email arrives.