R6220 has issue with internet

Hi all,

I bought this model yesterday and try to use it along with my Netgear CG3100D-2 with Naked Cable from Telstra.The reason i bought is i want to control the internet usage for my house mate via QoS function. And I have followed the instruction in the manual. After setting up, I have turned off the wifi from CG3100D-2, but the internet from R6220 was dropped constantly and also it was very slow. Any helps will be appriciated. 

Thank you