After software upgrade 9.3 my phone is requesting iCloud login, but my phone is connected to the other iCloud for a long time.

Hello. I am sorry for my bad english.

After software upgrade 9.3 my phone is requesting iCloud login, but my phone is connected to the other iCloud for a long time.

I remember the old iCloud's password and the new iCloud's password, but the system doesn't accept neither of them.

On the site www.icloud.com I checked if my phone is attached to the old iCloud, not tied . The new iCloud I removed the device in the " Find Iphone", but I still do not miss to register. What should I do?