Shell Black has a really great blog post explaining what has happened with the different Developer Certifications but in short the Dev 401 will be retired in the next few days. The first paragraph here explains what is happening to the Dev 401 and how it is being changed:
On June 18th, 2015 Salesforce sent an email to existing Salesforce
Certified Developers letting them know that a beta program was being
put together for a new certification – Salesforce Certified App
Builder. Just as the Salesforce Consultant certification morphed into
two new certifications back in 2011 (Sales Could Consultant and
Service Cloud Consultant), the Developer track was being split into a
declarative "button click" App Builder certification and a true
programmatic "coder" track with two new certifications supporting that
path: Salesforce Certified Platform Developer I and Salesforce
Certified Platform Developer II. In that email, to help with the
confusion, Salesforce published an App Builder Certification FAQ.
Although not directly related, it might be the reason you haven't heard back yet. Since they will no longer be offering this exam, they may have you take the app builder exam instead. If there is a number to call I would definitely call otherwise try the success community Salesforce Training and Certification group and/or reply to the case email you received and request an update on the case status.