No chance to log into phone after factory reset - old gmail account is not acceptet

Hi,
i got marsmallow update 6.0 over the air to my unrooted phone a few days ago. There something was not right with the system after that. Home button not working any more and so on. So i made a factory reset.

Now i want to start my phone for the first time again and do all startup thing. I can enter the formerly used gmail account, but the phone is not accepting it. There i get a message, this was not the right account used before.

But i only used one account on the phone, i bought it new and only one account was used since this time.

I wanted to remove the phone from my gmail account, but this was not working.

Can someone help me? How can i get access back to my phone? I think, the marshmallow update over the air was not made correctly and so it doesn´t know my account (perhaps???).

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