Flashing in the IMEI is something designed to be exclusively installed by carriers and makers. It's a shame they wiped it out.
You should ask this in the XDA Forum and Howards Forum as few don't believe what they found on google or here.
-> There is possibility they damaged the radio section.
I sold a Samsung Galaxy Note 3 SM-N900A to someone online. The LCD was bad so I did a hard reset of the phone but forgot to remove my google account. The person who bought the phone installed a new LCD but was locked out. So instead of contacting me to help, they decided to try and root the phone. but lost the IMEI number and Base Band. Then they returned the phone back to me claiming it doesn't work and they removed the LCD possibly so I couldn't see what they did. I purchased a new LCD so I could refurbish it but once I turned it on it powered up and showed me a pad lock unlocked logo underneath it said custom. after it loaded in the settings under about device I noticed base band saying UNKNOWN, IMEI was also saying UNKNOWN so i dialed *#06# and that said "null/null" I used Odin and the 4.4.2 stock rom to flash the firmware everything went smooth and no more padlock saying custom.... however the imei and base band are still saying UNKNOWN. any help to get this back on track so i can use it would be great. I am not a noob but I am also no expert so please provide instruction if you can assist me. thank you in advance...!!!

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