Phone rings and no one on other end of line. Getting to be a real pain in the [***]. This number calls at least once or twice every week and is getting to be a real nuisance.

More calls are the price of poor phone discipline.  No one answering can mean someone is pinging for live numbers or that the scammers are busy on other calls.   Don't worry, they will call back, and keep calling back until you take your phone back by blocking the calls.

Do not pick-up calls from unknown numbers/names.  You will only get more calls.  Calls from unknown numbers/names can be treated with prejudice.  If someone is hiding their identity, you can assume they are up to no good.   Do not fall into the trap of wanting to know who called.  More numbers are "spoofed" (faked)  as are the names, company names and addresses.  These are crooks and con-men.  When you call back to find out who called, you are verifying for the scammers that they have reached a working number and a person who will call back.   This info is shared.

The Do Not Call register is not protection against crooks.  They don't obey the laws about calling.  Many of them are outside the USA in any case.