Need Help C3000 - Phone cannot connect to internet

[seeseewhy]

Hi Guys Need Some Help Here.

I recently purchased a C3000 modem/router for wireless connection.

I purchased and activated the device on 11/3 and everything was fine.

Strangely, over the last weekend all of a sudden all our phones (iPhone X, 6 Plus) cannot connect to the internet.  Although the status show connected, but we can't access the internet via the phones at all.

And now the same issue has spread to our Roku device.  However, both of our Laptops (Asus, Microsoft) CAN connect to wifi still and works well. Anyone has any idea on how to apporach this? any advice is much appreciated

I have tried the following attempts:

- contacted my ISP, from their end the modem works fine and receive signal

- restart both the modem and the phones multiple times 

- reset my modem to factory setting

- from my phone, forget network and reconnect

- change connection name 

[FURRYe38]

What channels are you using? Auto? Try setting manual channel 1, 6 or 11 on 2.4Ghz and any unused channel on 5Ghz.
Any Wifi Neighbors near by? If so, how many?

What security mode are you using? WPA2 and AES is recommended...

What are you using for a SSID name? Should be something unique and no special characters in the name. Just plain text name.

[seeseewhy]

Thank you, I have tried switching channels and it still doesn't seem to work.

My security setting is already WPA2 and AES

[FURRYe38]

What happens if you temporarily disable WPA2 on the modem and see if the phone connects to the OPEN SSID name? Re-enable WPA2 and AES after testing.