Hello DallenTaylor. Security changes were implemented last year to prevent non-owner accounts from having unknown or unintended access to billing and network manager settings. In order to allow any non-primary accounts to have access to billing you will need to use the Owner account for your Mediacom account found here: http://support.mediacomcable.com/#!/RecoverId
Once you have the Owner account logged in you can immediately access billing or to enable your user-level account you can go to https://support.mediacomcable.com/Settings then click 'ID Management'. From there, click the word 'User' in the Role column for the account you would like to enable billing access to. Once you have the options open for that user ID, select Admin from the drop down box then click continue to save.
