There is only one course open to you.
Buyer opens s NOT AS DESCRIBED CASE!! He must not open a not received case as he received something if only an empty box.
Once opened it is up to you whether to provide a return label or just refund. Failure to do anything and buyer could escalate to ebay after 3 days
Buyer could be trying it on, but impossible to prove.
Whether you would have any luck trying to claim on whoever you used for delivery I do not know.