Hello horacio-aarhus,
You came from the best resource for issues signing in to iCloud: If you can't connect or sign in to iCloud
If the problem is receiving the verification codes, see these related steps on receiving them: Get a verification code and sign in with two-factor authentication
As you work through these, pay close attention to what it's asking for specifically. Is it asking you for this iPhone's passcode and the verification code? If so, then you'd need to enter the new password and the passcode to your iPhone (to unlock it). This can often be missed as you go through the steps.
In case these don't help, what did you mean by, "Are you only half an iPad with a different iCloud account"? Are you signed in to another Apple ID or iCloud account on this iPad? The more we can understand, the better we can help out.
Take care.