I understand that you facing issues related to new mail ID.
You can create the user mail ID only if you have sufficient licenses in your domain.
To purchase the license from the Customer Portal Kindly follow the steps below.
Step 1:Login into the admin console using super admin credentials
Step 2:Click on the Billing icon and click contact reseller to modify order;
Step 3:Login into the Customer Portal with the super admin credentials.
Step 4:Enter the required number of license you wish to add to your domain and click Next
Step 5:Make the transaction and once the transaction is successful the required licenses will be assisgned to your domain Refresh the browser
Step 6:To create the user email ID follow the steps mentioned in the link https://support.google.com/a/answer/33310?hl=en.
I hope you will be performing the steps as mentioned above,If you feel any difficulty kindly reply to your mail we will surely assist you in much better way.