Ask UK

"Please take my number off your list." and hang up. Any company that follows the OFCOM rules is obliged to honour verbal requests for removal, so that's the correct thing to do.

Admittedly, a cold calling company that follows the rules is an oxymoron so I tend to just cut them off with a "for fuck sake", hang up, Google the number out of sheer curiosity, and then add it to the block list. Every now and then I see a number in the call history that's been auto-blocked, so that at least provides a little satisfaction.

Or there's the Google call screening thing, though legitimate callers find it confusing and often hang up before you get chance to take over the call, or assume it's voicemail and try to leave a message.

I mean, I was good with people hanging up during the spiel. Saying "sorry I'm not interested" is more than fine and likely to put you on the upper end of calls that's day. Swearing or getting upset isn't acceptable and fails to recognise that neither of you want to be on that call.

However telemarketing has a better response rate than paper based surveys, and the data is used to drive decision making. A lot of people complain when things don't work out for you - like local council decisions on new amenities, but if you don't submit your opinion you can't be heard. It's not perfect but it is used to define a surprising number of things.

Wrt to you MIL, yeah, it's not nice to be on the recieving end of hostility, I get it can be annoying but as I implied above nobody chooses the job, I personally had to take whatever I could get and I was too young/not out of work long enough for JSA (plus JSA is a pain to get anyway, but that's a whole different story).