Who called from 3010000000

Recieved call about starting home business. Never have I inquired about starting home business. Caller had trouble saying my name and talked real fast. Finally told them I was not interested and to take my name and number off their list and to not call again

I keep getting calls on my cell phone (3-4 times a day) from 301, or sometimes +301...nothing else, no other numbers, just the 3 digits. I do not answer, and now have to screen ALL my calls.

I have also gotten calls from this 301 and nothing else after it number. Who are they?

I have also gotten calls 15 times in a night regularly from this +301 and nothing else after it number. Who are they?

I also got the phone call from +301 and after few min from unknown number.  Who are they?