software update unavailable (ios 9.3.3)

Hello

2 days ago my phone stopped receiving a network signal. It works fine with wifi but I can't make or receive calls or tets (except iMessages). My network said it would be recitfied if I installed the latest ios update which I had put off for a few days. I tried to instal ios 9.3.3 (currently running 9.3.2) and it got stuck on 'verifying update pop up' for about 18 hours. In that time I tried to shut down the phone but the lock screen was stuck on locked so I couldn't use it or reboot it but could see wifi notifications coming through in the background so phone was operational to a degree. Today I did the hard reboot (holding the sleep/wake button simultaneously with the home button) and the phone is now unlocked but still receiving no signal and when I try to install the update it gets as far as getting me to agree to Ts&Cs and 'verifying update' and then I get the pop up:

'Software update unavailable:

Software update is not available at this time. Try again later.'

I have tried this in excess of 20 times over the past 10 hours or so.

Any suggestions would be very welcome please as a phone that can't make or receive calls or texts is not very useful!!

Thanks in advance!