In this situation, the scrum master has already escalated the issue to upper management without resolution, so it's important to collect empirical data to further demonstrate the impact of the external dependency. This data can be used to show the consequences of the dependency on the project's progress, helping upper management understand the severity of the issue. By influencing management and making them accountable for ensuring the external team delivers, the scrum master helps ensure the problem is addressed at a higher level, which is critical for long-term resolution.