What did they ask of you before they could reset the appleid password?
I'm in a similar situation right now. Restored an Ipad2 thinking it would be like before where there's no Activation Lock.
Already talked to Apple support but all they could do is let me try to answer at least 1 of the security questions. I think they can only try up to 3 times then I have to wait for 8 hours and either they'll call me or I them to have another go at guessing it.
Truth is, I didn't take that AppleID setup seriously when I created it just for setting up this iPad so I am not sure what nonsense I put in the security questions.
Forget about proof of purchase as this was handed down years ago.