1) From your Portfolio account:
Once logged in into your Portfolio account, click on Edit your Settings located on the Toolbar, then head over to Your Account -> Manage Your Account.
This will take you to https://accounts.adobe.com where you will be able to find your billing history under Plans and Products -> Manage Plan -> Billing History.
2) On accounts.adobe.com:
You can also directly log into https://accounts.adobe.com with your Adobe ID, and then find your Billing History under Plans and Products -> Manage Plan -> Billing History.