Check output of ls /etc/init.d/*mongo* and service --status-all to find out exact service name
You must know what init system used in your system.
Googled for you:
https://wiki.debian.org/Init#Determining_the_init_system
From your link (https://www.mongodb.com/docs/manual/tutorial/install-mongodb-on-debian/):
Recent versions of Linux tend to use systemd (which uses the systemctl command), while older versions of Linux tend to use System V init (which uses the service command).
You can start the mongod process by issuing the following command:
sudo systemctl start mongod