iphone 7 doesn't respond

hi

a few days ago my phone stopped responding all of a sudden, it showed "no service"

at that time it was still on and i tried to turn it on and off for a few times but it didnt help.

it told me i have to update my software so i downloaded it.

after it was downloaded i couldn't update it for some reason, but it offered me to reset and then to update so i tried but it didnt work either.

now the phone is reset but i cant operate it, and i also cant update the software through itunes.

any advise?

thanks