Thank you for confirming. If both numbers are on the same internal account at our end, you would only need the one set of login details and both should be shown on the same online account.
If you have two separate internal accounts, you would need completely separate login details. If this is the case, we would need to delete one of the duplicate accounts so you can create it again with new details.
Do you know whether your two mobiles are on the same account or separate?