This is a Vietnumber Fake Phone Company. It calls you everyday with a different phone number each time. It will leave a message on your private phone.These are a bunch of jobless vietnamese girls trying to steal your credit card number. It will try to sell phone service to vietnam for 3.5 cents per minutes. Dont be fool by the cheap rate. This phone company doesn't have a prepaid phone card.
This company is so desperate for customers. It will open a yellow book and starts dialing your number everyday. Be ware this is ID theft company trying to steal your credit card

They call almost everyday from a different phone number, when I call to ask them not to call me, they hang up. Make sure you report them and maybe they will stop. You can do this at https://complaints.donotcall.gov/complaint/complaintcheck.aspx

You can report them at https://complaints.donotcall.gov/complaint/complaintcheck.aspx 

It takes a while to get them to stop, but report them each time they call from every number they call from. If everybody reports them they may have to pay a stiff fine and change their calling practices.

Thank you very much for your advise.  I have had the same problem as you described.

The callers are Vietnamese girls trying to steal your identity.  If you call them back, then they would hang up.  Thus, they know that you exist.
The next step that they would do is to forward all your mails to one of their mail addresses.  Here are two of their addresses:

9851 BOLSA AVE, SPC #163, WESTMINSTER, CA  92683

8742 STANFORD AVE, APT 4, GARDEN GROVE, CA  92841

Both addresses are in Vietnamese community.

Once they receive your forwarded mails, they would try whatever they can to gather much information about you from your mails, such as credit card numbers.  Then they would go shopping using your information or sell your information to others.