Some carrier-exclusive firmware versions are harder to crack. If the standard TalkBack/SIM methods fail immediately, check your firmware version in Settings (if you can get in) and look for specific security patch exploits relevant to that date.
The FRP lock has been successfully cleared, allowing total system access to the ZTE Blade A73 without needing the original Google account credentials. If you would like more assistance, let me know: What exact is your ZTE device running? bypass google verification on zte blade a73 exclusive
Restart your phone and proceed through the initial setup wizard. Some carrier-exclusive firmware versions are harder to crack