Malware Issue?

I recently upgraded to Fibre and since installing a new wireless router, all our devices (2x Iphone ani IPad Air) are experincing issues when surfing the net. When WiFi is enabled on the device and we try to visit any webpage it quickly redirects to either a **** site or a the App Store where it highlights a Hotel Book site app to download.

Looking at the web history and this redirection seems to be controlled by www.trafficoptimsr.com.

The issue does not happen however, on the IMac which is connected to the same Wifi network.

Can anyone suggest what is causing this but more importantly, what I can do to resolve it?

May thanks