A-Z help please , tracking is showing as delivered but claim made against me

Hello everybody

I am after some support please, an order has been sent with tracking , Royal Mail websites are confirming delivery but the buyer has started an A-Z claim for non delivery. and amazon refunded the buyer from my pocket

I have appealed the decision , my concern is how this can even be processed as a claim if the delivery has been confirmed?

any help/support wold be appreciated.

regards