i have receive a phone call from them, and said that you are a winner, but i don't beleive them

that's a bogus check. If you deposit it, it will take some time for the bank to make that determination.  But they will and when they do, you will be held responsible.

They sent me $4800 by check to pay for "taxes" on my $480,000 award. I'm supposed to deposit it and send $3800, via an instant cash service, to a "tax agent".