You gave me the wrong change.
mi a DA-to il RE-sto zbad-LYA-to
Politely pointing out that you received incorrect change.
Raising an error about change is a legitimate and important consumer right. In Italy, it should be done politely but firmly. Cashiers are expected to verify discrepancies. If the error is minor, Italian culture sometimes allows letting it go (lasciare perdere), but significant errors should always be raised.
Ho dato un biglietto da venti — aspetto cinque euro di resto.
I gave a twenty-euro note — I'm expecting five euros change.
Stating what change is due
Scusi — credo ci sia un errore nel resto.
Excuse me — I think there's an error in the change.
Very polite way to raise the issue
Può verificare il conto?
Can you check the bill?
Asking to recheck the entire transaction
Italian law requires cashiers to issue a fiscal receipt (scontrino) for every sale. The receipt is the primary tool for verifying change errors. Modern POS systems calculate change automatically, reducing errors, but manual handling still occurs with cash-only transactions.