It sounds to me you have 1 or 2 Sky Q boxes that are transmitting on the same frequencies as your routers wifi. This is a known problem which throttles the Vodafone router bandwidth to next to nothing.
The best thing you can do is manually set the 2.4Ghz and 5Ghz frequencies on the Vodafone router to different frequencies, making sure you are also not using the same ones as your neighbours as well for better wifi performance. Use an app like Wifi Analyzer to see what channels and frequencies are being broadcast.
You will have to download an old version of the Vodafone Broadband app (4.1.0 or older) on Android to do this, I would also split the SSID's as well within the router for separate 2.4Ghz and 5Ghz networks.
Ripshod is also correct about Vodafone's DNS servers, because they have been at their limit and capacity for sometime this year. This is due to the amount of customers Vodafone have and they haven't upgraded their infrastructure adding more DNS servers to cope with all the DNS requests.
You can manually set the DNS servers in the Vodafone router GUI for your internet connection, make sure you reboot the router afterwards. I would use both Google and Cloudflare DNS servers 8.8.8.8 and 1.1.1.1
