D7000 I cannot throttle speed, on VDSL

[Camster2000]

I live rural and we will not get fibre until 2021. I am on VDSL so brought the nighthawk which is still great as I can get netflix on HD. I have a panasonic 4k TV which means that the pictures are very good. All was great but three weeks ago we could no longer watch Netflix, watch youtube nor play on Xbox one X. I know, 1st world problems right. The LAN light is red but the TV states it can get internet. I tried it on wireless same issue. changed the cords, same. Noticed that when looking on TV screen and streaming starts the resolution goes from HD to 4k every time. I cannot stop this on the TV but my cousin said the modem can, but doesnt. I cheacked the qos but cannot throttle the download speed. I am going spare. PS everything works fine on the HDtv and panasonic state it is a modem issue. Thanks guys 

[michaelkenward]

How fast is your internet connection?

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@Camster2000 wrote:

The LAN light is red but the TV states it can get internet.

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What LAN light? On the router or the TV?

The LAN lights on the router are colour coded:

The LED color indicates the speed: white for Gigabit Ethernet connections and amber for 100 Mbps or 10 Mbps Ethernet connections.

Is the TV connected by LAN or wifi?

[Camster2000]

The light on the modem when the modem LAN shows is red, more so than amber. Speed is any where between 12 to 15mb at a push so no where near enough for 4k streaming. Have also tried wifi though. Thanks for replying, much appreciated.