You can close down the server either with the script command or you can choose to kill it. The script command would be (when in the home directory of the TeamSpeak server):
./teamspeak2-server_startscript stop
You can also kill the server if the above command doesn't work properly:
kill -9 server_linux
You can check all the processes running on your box and whether TeamSpeak has closed down properly with:
ps -ef