It's left to the Agent's discretion. Personally, I tried to vary methods, so I might e-mail twice and leave a voicemail once. Even if the ticket was closed, there's an automatic alert (outside control of the Support person) that sends a message about the ticket being closed and there's a customer satisfaction survey (or there was) attached to that message. If you're not getting those alerts, you may want to make sure your contact information in the Customer Portal is correct (I saw a lot of customers who put in bogus e-mail and/or phone information, maybe to avoid sales calls, but it meant that Support was handicapped reaching people too).
Edit: Also, if you have multiple SWIDs, make sure the SWID you open the ticket under is the one with current and accurate contact information. Good info on SWID X does no good if your LEM license and LEM support tickets are under SWID Y.
This all supposes that the ticket is actually an issue ticket. Other tickets are handled different ways. For example, with Feature Requests, Support is directed to gather as much information as they can, escalate that information to development and/or the Product Management team, and then close the Support ticket. If dev needs more information, they'll re-engage with Support to communicate with the customer. Otherwise, you'll need to wait for your new feature to show up on a Road Map or in a connector pack.