Deleting Virtual network (classic) fails with500

I'm trying to delete the last existing resource from a subscription but it fails with 500. Also just accessing it via the portal gives a 500. Deleting the resource group also fails with 500.

{ "shellProps": { "sessionId": "xxxxx", "extName": "Microsoft_Azure_Network", "contentName": "ClassicVirtualNetworkBlade", "Resource ID information removed for privacy"": " information removed for privacy"/resourceGroups/Default-Networking/providers/Microsoft.ClassicNetwork/virtualNetworks/IBN-Netwerk" }, "error": { "message": "The classicVirtualNetworks resource was not available", "code": 500, "details": "The classicVirtualNetworks resource is unavailable, please try again later. Status Message: Encountered an internal server error. The tracking id is 'xxxxx'." }}

It can't be connected to any other resource because it is the last one in the subscription.

Executing: Remove-AzResourceGroup -Name Default-Networking -Force

gives:

Remove-AzResourceGroup: Long running operation failed with status 'Conflict'.

StatusCode: 409

ReasonPhrase: Conflict

OperationID :

How to get rid of this last resource?