Not just bank employees, we don't hesitate to give our mobile number to anyone let's say we go for a paid parking there we have to leave our contact number for our bike or car which is mandatory, or we go to shop like electronics there we ask for our name address and contact number for billing so our information is wide available than just banks but I do agree though, the spam callers really target their audience for example I recieve lot of spam calls regarding credit card offers, insurance, personal loan and I assume this is happening cause CRED app is leaking my CIBIL score to everyone.
I agree that is why I have kept two mobile numbers wherein one is a postpaid connection which I have been using since 2015 and all banking-related services are connected with that number. The other number is a prepaid one which I give when I am asked at a shop or for other matters. Whenever I get a spam call I block them either with my inbuilt phone blocker or true caller. Still, these spammers manage to call me again with their alternate numbers which is pain again as I have to go through the blocking procedure.
Yes, this is also what I follow. I had purchased a separate number in 2019 for banking as my existing number was flooded by spam calls. But unfortunately, even though both of my numbers are DND, I at least receive 4 to 5 spam calls everyday.
There is no resolution to this unless the government becomes strict. Even though the DND registry is here since a long time, no one really follows that. Unfortunately this is how majority of the government services run in India.