Hmm that's quite odd. In my experience those mod vendors respond quite fast on my e-mails. It may somethimes take up to a few business days as they are very buy. But they do respond on the e-mails.
In case if you purchased it at WebsiteCM, the best thing to do is post a ticket at their support system.
http://www.websitecm.com/support/index.php
I just checked the website of Cart-Lab again, and when you try to add something to the cart, it says shop closed. It happened before that Cart-Lab's shop closed temporarily. Maybe he just needed a break for a while. And therefore you can just contact the other mod vendors who are reselling cart-lab mods (websitecm and bcse).
Best way to do this is posting a ticket to their support system, instead of just a regular mails. E-mails are somethimes overlooked, tickets in their support system usually not.