If it is a business name, and the business name is registered, you may be able to get it back using the domain name protection described here:
netlaw.de 98/02 - Domain Name Disputes in Germany
It might be worth reviewing this, and others (I Googled for 'domain name protection Germany') to understand the rights of the company and then write a formal letter to the new holder, as well as the appropriate authorities. You probably won't need a lawyer, but if you have a friend that is a lawyer, you could have the letter come from them.
Good luck.