I buy used IPad mini

That's nice. What's your question?

If you're encountering Activation Lock then there's nothing you can do without the previous owners credentials. The device is useless to you. There is no way around it.

no. I already said there's nothing you can do. Return it for a refund if you can.

iPad is in Activation lock mode. Without the original users information, it will be impossible to activate and use that iPad.

Return to wherever you purchased from and get all your money back.

You purchase a high tech door stop.