Note 4 AT&T N910A boot Loop

i was playing with mobile , mistakenly i press *#9090# code
there were option Diag i clicked on that option and i didn’t know what option is selected from there suddenly phone restarted and phone continuously restarting from that time , when phone on i repress code *#9090# code
there were only option ( SERVICE)
i hard reset phone didn’t solve issue . i re flash phone with same OS as previous installed n910aucu1coc4_n910aatt1coc4_att_android_5.0.1
now phone says android is upgrading and its being restarted .
recovery and download mod are okay .
please help me its totally new phone