Who called from 9898871678

This is the third time this month, the person is selling coins.I could  not under his name or the company he works for. He does not leave a message or has he sent me information on the company  in a January conversation With the caller. I am   getting way less calls then before I had it

How do I block this number from calling again?

Google is your friend.
Try "phone blocker"
(Without the quotes)

I received a call from a guy who said his name was David (clearly a foreign accent).  He said there was a problem with my computer and Windows 8.  He said I had to turn on my computer right away so he could help me correct the problem.  I said, "I hate to disappoint you, but I don't have a computer!"  He continued trying to tell me I did.  He asked if I've ever had a computer with Windows 8 in this household.  I told him, "No!"
I hate these calls especially when I'm on a "Do Not Call" list.

Consider maybe getting a call blocking device or phone.. You can google them and many are around $60.00 or so.