Hi Mike,
Please carefully follow the instructions below and add a comment below with your results. If it doesn't allow you to open the case please describe what happened and I'll assist you. I've had people do this many times with success.
Please create a New Support Request in the portal and choose Issue type: Billing Problem type: Refund request, then click Next. Once it shows suggested solutions, DO NOT CLICK the Request a refund button, click Return to support request in upper left corner as shown below:
Click Next, continue filling out information, make sure your email/phone are correct, and finishing creating the case. There is no charge for billing/subscription management support requests. A support engineer will assist you with your refund request.
Please click Accept Answer if above was useful. If you have issues submitting the case please add a comment below with details.
Thanks.
-TP