Disculpe,
creo
que
me
dio
de
menos.
dees-KOOL-peh, KREH-oh keh meh dee-oh deh MEH-nohs
Excuse me, I think you gave me too little change.
'Dar de menos' means to shortchange someone. Starting with 'disculpe' and 'creo que' keeps it polite and non-confrontational.