Called me with this number and said I'm a possible winner of some type of a sweepstake.

No.
If you did not enter that sweepstakes, you cannot be a winner.

this  number called my cell twice. voice mail was just a weird tone. i called back from a land line and it said "this account number is not valid". i blocked the number from my cell phone

Received a phone call from this number saying I'm a possible winner of their sweepstakes too! He said I "registered" online at "reward zone" and need to register over the phone. Told him he has the wrong number so I just hung up. I never entered any sweepstakes online.

Received the call on my cell. Male caller said he was from "Publisher's Service" and that I'm a finalist for some sweepstakes. I just hung up on him.