Good to know
The reply looks the same whether or not a purchase exists on the address you enter — that's deliberate, so the form can't be used to check whether someone is a customer.
Once you have the key again, activate it on the pricing page for this website, or in the Chrome extension's Settings page for the extension. If the key says it has hit its activation limit, remove it from a device you no longer use first.
Stuck? Email support and a human will sort it out.