iPhone 6 Plus Wi-Fi not working with Wi-Fi Multimedia enabled on router

I have an iPhone 6 Plus and recently the internet has been very slow or not working at all on our Wi-Fi at home. After much tinkering with settings on the router I discovered that if I disable 'Wi-Fi Multimedia settings' on the router the internet works fine on the iPhone but is then very slow on my laptop.

Apple themselves state that you should enable Wi-Fi Multimedia on your router for the internet to work correctly on Apple devices. However, the internet is not working on my iPhone with Wi-Fi Multimedia enabled on the router - the internet is only working when I disable Wi-Fi Multimedia.

My router is a Netgear WNDR3700 v4 with the most recent firmware installed on it.

Can anyone help with this? Merely disabling Wi-Fi Multimedia on the router is not an option as then the internet does not work correctly on other devices.

Thanks,

Pedro