Why am I receiving the same invoice mail twice?

It's because your account is configured to send invoice mails to both the contact person, which is you, and a specific email address, which is also set to be yours. You can change this in the "Your company account" tab in the settings. The invoice mail settings are located in the invoice section of the tab, below the invoices. For example, remove your email address from the "Send invoices to this email address" field. You must be administrator in Scrumwise to change these settings.