Need help to unlock SM-G890a android 7.0

Good day everyone. Im not sure which binary is my unit. I have a unit here that needs to be unlocked. Its sm-g890a with os 7.0. firmware version is G890AUCS7DRB1. Tried unlocking with z3x but all failed. I tried flashing combi file from z3x but then it gave error so now unit cant boot normally. Im still downloading full firmware to revive it back.

Now my question is which modem would work with my phone? Need guide as to how to unlock this unit. Thanks

[ 4/5/2018 4:55:00 PM ] Searching Samsung modem... detected COM10
[ 4/5/2018 4:55:00 PM ] Reading phone info... OK
[ 4/5/2018 4:55:00 PM ] Model: SM-G890A
[ 4/5/2018 4:55:00 PM ] AP version: G890AUCS7DRB1
[ 4/5/2018 4:55:00 PM ] CSC version: G890AATT7DRB1
[ 4/5/2018 4:55:00 PM ] CP version: G890AUCS7DRB1
[ 4/5/2018 4:55:00 PM ] Product code: ATT
[ 4/5/2018 4:55:00 PM ] Phone SN: R38G9077DST
[ 4/5/2018 4:55:00 PM ] Unique number: 06157DF690AE0328
[ 4/5/2018 4:55:00 PM ] Reading IMEI... OK
[ 4/5/2018 4:55:00 PM ] IMEI: 352xx (SIGN: NG_SIGN)
[ 4/5/2018 4:55:00 PM ] Reading data from phone... error (0)
[ 4/5/2018 4:55:00 PM ] Try downgrade modem if possible

error in flashing this combi file

Code:

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COMBINATION_ATT_FA50_G890AUCU6AQC1_ATT6AQC1_CL6309376_QB12821437_REV02_user_mid_noship.tar.md5

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[ 4/6/2018 10:43:00 AM ] File analysis... OK
[ 4/6/2018 10:43:00 AM ] Total file size: 0x39455AF0 (916 Mb)
[ 4/6/2018 10:43:00 AM ] Searching USB Flash interface... COM35 detected
[ 4/6/2018 10:43:00 AM ] Setup connection... OK
[ 4/6/2018 10:43:00 AM ] Reading PIT from phone... OK
[ 4/6/2018 10:43:00 AM ] Sending sboot.bin... error timeout