Sorry to hear that, if you have tried multiple headphones with no adapters in between then there may be something going on with the module.
Warranty and non-warranty claims are not handled here on the forum, but I can point you in the right direction! Here are a couple of options that you could choose from:
• Submit a Warranty or Service inquiry with our Technical Support team by logging onto the http://www.alesis.com/support“>Alesis Support Page. Select Warranty or Service Inquiry from the drop-down menu.