Galaxy Mega 2, sm-g750a, Is there any way to fix my IMEI ?

I used my galaxy mega 2 on AT&T's network for about 4 months without any problems until I decide to root it with either Kingoroot or Kingroot and since then i've been network blocked because it changed my IMEI. I want to change it back to what the sticker under the battery says but have had no luck. So far i've tried flashing it using odin and the z3samsung tool. It was 4.4.4 but now it's 5.1.1 KitKat because I can't try to downgrade because the "repair" firmware 4.4.4 always fails. The bad IMEI 350050500009692 i was told that this imei was a default when your imei gets erased by some mobile tool pro via email. I won't publish the good/true imei that's on the sticker. Baseband G750AUCU3B0H4 , Build number LMY47X. G750AUCU3BOH4. Also I get an error when using the z3tool to write NV data, it says "security damaged". Being the bright person I am I didn't back up anything prior to the first attempt but all I need is the IMEI restored everything else seems to work fine. I'm stumped and need help.
Thanks to all or anyone

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