Its registered in Finland simply go to the financial regulator of finland website you will find the address
Make sure to find the company name first a company name doesn't mean the domain name.
Go to the website below type in localbitcoins you will get all
That's their mailing address (same as on the website), it's a virtual office as required by the Finish law if you don't want to disclose or you don't have the need for a real office, and judging by the number of topics here and the way people are reacting to their problems I can bet that they will never disclose the real workplace. So if you go there and ask for them you will just be pointed to a box where you can leave any letters or citations to them, no way you're going to see the CEO with a coffee walking down the lobby.
I list a very huge amount more then a normal person earn in a a year. I will pay money to hunt these scammer down and even their children.
Just a suggestion, if you use the same tone and the same threats in your discussions with them even the ombudsman will decline your case as they will deny involvement when there is no cooperation from the accusing side and you don't follow standard mediation procedure, especially if you're the one doing the death threats. For what it is you might actually get yourself in trouble if they file a complaint against you.