You really should send them back; for all you know, the company meant to send those two extra to other people.
You'd be doing something most people wouldn't.
This is the third they sent me other a spam of three weeks.
When I got the second on the fourth day after the first, I contacted them about getting an extra. Still no reply.
Since then Ive sent 3 messages all apparently unheard.
Seems they don't want them back.