Anyone know what to do about a company using your brand/comapny name in their own domain name.

I have come across a company using a domain name with my companies name in it, but it is being used in a subdomain, of their own domain name.

eg www.mycompanyname.theircompanyname.co.nz

I know you can get a domain back if they have used my company name as the primary domain, but what can you do about it when they create a new subdomain of that primary domain, using my own company name as that subdomain. I do have a trademark on my company name,

 

Any domain name experts out there on what to do in this situation?