They are not all from India. Everyone I've actually talked to is American. Whether they are real insurance agents or just trying to steal your data is another matter. Medicare rules prohibit cold calls or signing a client up on a call generated by an agent. Obviously they don't care. Search cold call Medicare on google, there are ready made scripts for these people.
While some of these calls are obviously Americans, I have suspected for some time that a lot of the calls form India are the result of list "sharing" by all the tech support / customer service boiler rooms used by American companies.
I vote for cutting off all incoming calls from India until their government cleans up their act.