Hello,
We have the same problem. Did you already fix it?
Looks like WaaSMedicSVC turns the service back on, even when it is disabled.
thegeekpage.com/windows-update-medic-service-waasmedicscv/ shows more about this.
We are testing it now, but the site states it wil turn on again, so we have to see how long it works. I will keep you updated.
Can We Turn Off the Windows Media Update Service?
Yes, if you want to disable the service at any time, you can, but when you try to disable it through the Service manager, it gives you an Access Denied prompt. Also, service is disabled only temporarily, as the Windows OS automatically turns the update on at some point.