Sorry to hear about the recent issues you have been experiencing.
You can find your Studio One product key by visiting My.Presonus.com. Log in to your account. Go to Products > Software > and select Studio one. Here is a screenshot of it on My.Presonus.com:
If your key is not there, it could be that you have an account under a different email address. Please submit a support ticket to technical support to resolve. Please include any previous email addresses you may have used.
Here is a link to create a ticket: http://support.presonus.com/hc/en-us/requests/new