That limit is per month?
I have my two computers connected using Wifi to the Wifi device. This wifi device is connected with a USB cable to the router of the telephone company.
The router has IP 192.168.0.1 and the wifi device has IP 192.168.0.100
If in the browser I write as URL the IP you enter the device or are asked login (you configure that). I have these two devices configured with login.
Then you can see in each device the computers that are connected at that moment.
In my wifi device I see two computers connnected: “core2” and “quad” are the names. Correct.
In the router I see four computers connected: Correct too. Because one of them is “core2” and the other three are “quad” “Quad” and “quad”. The explanation is that in my “quad” computer I have three OS: ubuntu12.10, linuxmint14 and windows7 and everyone has “quad” as the name (probably the one with the uppercase “Quad” is windows).
So you can see in your devices who is connected. Also one of the devices, I don’t remember if it was the wifi, didn’t had login configured, so everyone could enter and change it and make my wifi their own.
If you see that really someone is connected, the best way is to configure the device to let only connect the computers that have the MAC addresses you specify (it shows this MAC address with the computer name. But beware of using such thing because you can make a difficult life for yourself easily if you really don’t know what you are doing. Go always the easy way and only use high security when attacked is my advice.