Has anybody ever got packages containing one rubber band in the mail without ordering them?

Yes they're just companies advertising on a rubber band and not paper.

Did you order something? Preferably from Ebay? Ebay has a lot of scammers of both buyers and sellers. If you ordered then perhaps the seller sent you a rubber band just to have a tracking number that you got "something". Buyers often scam sellers by saying "Not received" if no tracking provided or "item didnt match desciption" resulting in buyer returning an empty box and collecting a refund from ebay. Be careful!