iPhone stuck on 10.3.3?

So I was told I had an update available for my iphone 7 (about a year old, 128GB) and the update is iOS 10.3.3 which is pretty far behind. When I click update on my phone an error message pops up that says I can't update because I am no longer connected to the internet. I have tried several different locations and different wifi connections but it won't update. I tried connecting to my computer and updating through iTunes (after updating iTunes to the latest version) and iTunes tells me there is no update for my phone it is up to date. I deleted iTunes completely and reinstalled it and it still does not work. I have 82GB free storage and the phone is only a year old, no damage to it great condition and I have never had any problems before. Any suggestions on how to get it to update? Thanks!