First off, you must learn how to stay online and not publish personal info on a public forum, anyone can snag those details and get in touch and try and obtain passwords from you.
Secondly, the big question is, is this the same phone that you sent out or not? Each phone has a unique identifying IMEI number on it, check that the one that you've receive dback is the one that you've sent out, then post another question here.
If it is the same phone, you will need to refund the buyer.
