Hi Mel,
You might want to setup account on ManageEngine support portal, should both be able to create new requests as well as follow your previous requests.
I do agree with you, would be very good if customers could purchase Premium Maintenance with much shorter SLA to use in critical situations.
You should always receive automatic e-mail with your request number when sending request to their support, possibly something is either not working on their end or if your company has a spam filter that might block it.
Hope this helps.
Regards,
/Thorir