Chestnut
I would second using the Telephone Preference Service, I've been using this for years. it doesn't stop them all but if I get any unsolicited calls I just block them.
You can also check who called you, where people put the details of callers and whether spam or scam. You don't have to register:
who-called.co.uk/
I don't understand why BT is considered expensive. I'm paying £22.05 for Broadband and £6.52 for the BT Vision Box making £28.57 a month in total. That includes a landline but I don't use it. Is that expensive?
I don't find that the TPS stops all calls and guess that spam callers some just dial randomly generated numbers and don't even think about checking the TPS lists. However it does stop most of them.
We were allocated a new number when we moved here which has never been in any directory - I do wonder if this makes a difference?
We have a holiday home and have a phone there in case of emergencies, though it's rarely used. We have broadband included in the cost too and it is around £30 for three months which is really amazing. They don't advertise this rate at all, initially we just had the phoneline, then we were asked if we wanted to add broadband. At the start there was very limited broadband included but then it went to unlimited during lockdown.
The rate for calls is relatively expensive but, since we don't use that aspect, this is not a problem.