I bought a iPhone 5c on Craigslist, I know not the safest transaction method out there but I was desperate after running my old phone through the washing machine... When I got the phone the guy showed it working on AT&T so I figured great it hasn't been locked. Before I went to the ATT store I decided to double check that the IMEI was clear, because my purchase was a bit sketchy. Turns out the IMEI was bad and the phone was listed as blacklisted. After getting no repose from the seller I decided to take it to the store and see if they could do anything about it. When I went to the ATT store to get a new sim he entered something on the computer to make sure it was valid on the network and it came back as clear. Everything works great except I do not have LTE. I spoke with a support representative online and she said they had my device ID wrong and they needed the IMEI to activate it. My question is if I give the IMEI to ATT will it cause them to blacklist my phone?