WNR 2200 setup for traffic controls

Hi everyone,

I would like to ask you for help to set up my wi-fi for traffic connection (limited per month 20gb)

My router model is WNR2200, I've tryed to lock Iinternet speed for MAC adrees in my apartment to save trafic for monthly surfing not for torrent downloading or somethins like this.

I know about QoS setting which is controlling internet speed by seting up priorities, but if nobody using the network, the lowest priority can use all trafic with max speed, which is bad for trafic connections.

Please give me an advice, how to lock internet speed for MAC/IP adress, for example 5mb/s permanently for device.

Regards,
Jack