can't sign into icloud on iphone 6
I had iOS 10.1 I believe on my phone and one day I turned it off and when I turned it back on, all my contacts were deleted off my phone and all my messages were just phone numbers. My phone also wasn't updating to iOS 10.2.1 until finally I synced it up to iTunes on my computer and I was hoping the update would solve the problem but it didn't. My contacts are backed up in my iCloud (I checked on the computer), so now the trouble is I can't log into iCloud on my phone in the settings. I'll type in the correct email and password and press Sign In and it'll say Verifying for a few seconds before it just disappears and returns to the regular screen with all my sign in information still typed in. So I would like to know how to fix it and be able to sign into iCloud on my iPhone 6 so I can have my contacts again.
iPhone 6, iOS 10.2.1