13-04-2022 15:13
Why does my broadband drop out when I answer my landline telephone. Openreach engineers have checked it about six times and say it is not a problem caused by their system.
13-04-2022 16:01
Have a nosy at this troubleshooting link
https://help.nowtv.com/article/fix-problems-with-my-phone
Can’t be much help as I am a broadband customer with BT. All I could suggest is to call the broadband team which I assume you’ve already done.
13-04-2022 23:03
This can happen when you should be using micro filters, and you aren’t, on one or more sockets.
I’m not saying it is this, but it’s the first thing I’d check.
This would be an issue on your side of the Master Socket, which is where Openreach’s jurisdiction (and troubleshooting) ends,
Check you are correctly set up as shown here, for whichever scenario is applicable:-
https://www.bt.com/help/broadband/why-do-i-need-adsl-filters--microfilters--and-where-do-they-go-