Licensing Issues - stolen license

Hi,
I offer your CMS product to my web design clients. I don't purchase a license for them, but rather I purchase licenses I can use myself then I charge them a fee for the customisation work, then they pay a small monthly fee to use the license.

Recently I had another website company transfer our clients site to another host without our knowledge. They are now using the system with our license but refusing to pay the monthly fee!

I figured I would deal with this by going to the CMS, logging in and updating the license key to an old one which had already been cancelled by Interactive Tools. This has been a fine solution in the past, HOWEVER this time it didn't work as I guess that license number is not blocked anymore?

I need someone to either reblock that license, or cancel the license in question and provide a new one to me that I can use for another client.

Thanks :)