The room has not been cleaned properly.
cor-ret-TA-men-te — five syllables, stress on the fourth.
A more precise complaint than simply 'la camera è sporca' — specifying that cleaning was incomplete rather than absent.
'Non è stata pulita correttamente' = has not been cleaned correctly. This passive construction is stronger than 'è sporca' (is dirty) because it identifies a service failure. 'Correttamente' (correctly) is an adverb formed from 'corretto' + '-mente'.
Il bagno era sporco quando sono arrivato.
The bathroom was dirty when I arrived.
State the specific time and room area
C'erano capelli nel bagno.
There was hair in the bathroom.
A common and understandably unpleasant find from previous guests
Il pavimento non era stato lavato.
The floor had not been washed.
Specify exactly what was not done
Cleanliness standards vary significantly between Italian hotel categories. 1-2 star hotels may have only basic cleaning; 4-5 stars have daily full cleans with premium products. If you experience poor cleaning at a higher-category hotel, report it in writing — it may affect your bill.