Unjustified bill from incasso?

A friend of mine that wasn’t in the country for the past 3 months came back and received a bill from incasso of a gasoline taking at a gas station that has nothing to with him, demanding a payment of over € 700 which he call to verify that the bill is real. What can he do? It wasn’t him as he wasn’t in the country at the time the bill was accumulated with proof.