No tak jsem pátrál trošku dál a našel toto http://androidtipguys.com/forum/how-unlock-android-tab-if-forgot-google-account-2953.html
píše se tam: Unlock the android device is only done by hard reset ,and this is
the only way to crack the account.Because if you enter the details
into the account then device required the internet connection,and there
is not at that time.

Hard Reset:

1. Press and Hold Volume UP + Power Key.

2. Then you see android logo

3. After that select wipe data / factory reset.

4. Then conform to yes.

5. Now reboot device.

6. See your device is unlock.

toto mi pomohlo kdyby někdo měl stejný problém