The NOW router is known to be rubbish, have you split the bands?
What about a reset or factory reset to the router by holding the reset button for 15 seconds?
Using the link I gave you can also check the status of your line.
Worst case call the team using the number from the link below.
Think of the Hub location: is it relatively high up and centrally located and not near any other devices that may cause interference? Even having it too close to a DECT phone can cause issues.
Do try the earlier suggestion about splitting the SSIDs. Also, if you have any devices that are only capable of connection on the 2.4GHz band make sure that you have the bandwidth set to 20MHz only and select channels manually from just 1, 6, or 11 to prevent overlapping. A WiFi analyser can help to identify which are the most congested channels in your vicinity so then you chose the one which is the least so.
What WiFi speed were you promised, and what WiFi speed have you got? (Hold a mobile phone with its 3/4/5G switched off as close to the router as you can, and run fast.com in a browser to measure this).
Have you got something, e.g. a laptop, where you can switch off the WiFi when it is connected over an Ethernet cable to the router, and run fast.com in a browser there? See if you get radically different speeds than over WiFi?
Please note, by the way, if you take the advice to split the bands, you should then visit every device you have that is on WiFi and capable of running on the 5G band, to ensure that it is running on one of the ten 5G band slots if it is in range of the Now router 5G signal, or running on the 2.4G band if it is out of range, or if all ten 5G slots are used up.
5G is less congested than 2.4G can be (which is why the most effective step to improve WiFi speeds is to use WiFi Analyzer as above, to ensure your 2.4G is on the least congested channel), but splitting the bands and then tweaking which band your devices are on may do something to compensate for the lack of device or band steering on the Now router, something that replacing the Now router with a better third party one, or using a mesh system, may bring.