I have an Azure App Service that contains 1 Web App with 1 slot. I have 2 instances assigned to the App Service. This week, the App Service shows about 60% CPU usage, and its
the commandlet you mentioned is not supposed to be used with the Azure App Service, but with the Azure Cloud Services and role model, so you do not need it here. Azure SDK 1.3 is very old as well, today the latest is 2.9.
Next, try to use Auto-Healing feature - it is difficult to understand why your web app is so resources consuming, especially if you tried to restart the W3WP (did you kill it in the Process Explorer of the dashboard?), so built-in feature can be helpful.
And you can find the webapp id and execute PowerShell, for example, Stop and Start it. If that will not help, i would suggest to re-create the instance.