I had the same thing (different company) for a fake GoDaddy invoice. When I went to support and tried to file a case I got the message:
We’re sorry, you can’t file a case on this type of transaction. Please refer to our User Agreement for more details.
I can't repeat the steps I took (now that the invoice is canceled) but this is what I think I did:
1. Went into account activity.
2. Clicked on "view details" for the pending invoice.
3. Was given the option the PAY or CANCEL the invoice. I clicked CANCEL.
4. Wrote an appropriate message to the account that sent the invoice, i.e. "**bleep** off scammer".
5. Clicked whatever confirmation button I needed to to send the message and cancel the invoice.
It now shows up in my completed activity as "Canceled – Invoice Received" and there is a strike-thru on the amount.
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