When you have multiple subscriptions under your Azure account; it's important that you are selecting the one you wish to operate on (and use this as default); to avoid accidents happening to resources on the wrong subscription.
Classic mode
Set-AzureSubscription
Select-AzureSubscription
Resource manager
Select-AzureRmSubscription
Subscription information
The commands above ask you to specify information (e.g., the Subscription ID) to identify the subscription you want to switch to. To list this information for the subscriptions you have access to, run this command:
Get-AzureSubscription