Do you answer calls from withheld numbers?

I work in a busy hospital outpatients and our phone number doesn't show up, you try to call people to offer them a sooner appointment to fill a cancellation slot, or call them back to reply to a message they left us and 90% of people don't answer and the ones that do are often defensive because they are convinced you're a cold caller and you have to try and quickly explain before they put the phone down but at the same time try to remain compliant with data protection etc people complain about NHS waiting times but so many appointments are wasted because a) people cancel at less than 48 hours notice which I realise is sometimes unavoidable but because often we struggle to refill them because for every 10 calls you make only 1 person will answer its extremely time consuming. I know cold callers are annoying but seriously, what is the big deal? just hang up if it's a cold caller! As someone rightly said earlier, there was a time when you had no idea who was on the line when you answered it back in the day when we all just used landlines. The laugh of it is that most cold callers these days that everyone is so desperate to avoid often have a visible number 🙄