This will possibly have no effect but could be worth a try.
Have you tried changing your IP address. If you switch off your Openreach modem if you have one or the Homehub if you don't have a separate modem for about 15 minutes you should be allocated a different IP address. If you are not allocated a different one try switching it off overnight.
I have changed my TV to use a (different) static IP Address and have tried both Open DNS and Google DNS. Still not working
gg was referring to changing your public IP address not your local one.
Here is an online meesage about this whole affair:
BT Broadband Users Suffer Problems with Netflix on UK Smart TVs
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Some of BT’s Broadband customers, primarily those who are trying to use the Netflix app on an LG, Samsung, Sony or Panasonic Smart TV, appear to be running into problems with getting the service to work. In many cases the app will return a UI-113 error, which has also been seen on some Humax based set-top-boxes.
The problem seems to have started in late January and several related topics can be found on the ISPs Community Forum. Some subscribers have been briefly able to circumvent the problem by logging into and out of Netflix while also resetting their HomeHub, although the fault usually returns and the same trick doesn’t work for everybody.
Netflix itself has a specific page for the UI-113 error, which simply states: “If you experience the error code UI-113 while watching Netflix on your device, it typically points to some information on your device that needs to be refreshed.” However the advice given by Netflix to resolve the issue (e.g. reboot the hardware, login / logout etc.) does not deliver a proper fix.
The error itself is actually a general one that has been seen in the past on many different devices, with different ISPs, and usually reflects a problem with connecting to Netflix’s servers (DNS related perhaps?). But so far this latest issue only seems to be hitting customers of BT’s broadband service.
A BT Spokesperson said (canned statement):
“We are aware of a very small number of customers using some smart TVs who are unable to watch Netflix via their television’s built-in Netflix app. We’ll support manufacturers with their investigations to help resolve specific problems.”
One of those manufacturers, LG, echoed BT’s statement and also added that they were “working closely with BT and Netflix to help resolve specific problems” (here). At present neither side seems to be taking clear responsibility for the problems and no ETA for a fix has been proposed.
I tried that unplugging everything for a long period of time, and it didn't work either
The static IP address you have allocated to your TV is on your own private network and is been issued by your router.
You do not have a static IP address with BT. It is dynamic and should change fairly often but it may for some reason have become "stuck". If you do as I suggested it should refresh and offer a new IP address.