Relay contact (switching) voltage
Since the maximum switching voltage is 250VAC/25A, can I use this
  relay to switch 380VAC/1A load?


You can't horse-trade current rating and voltage rating on a relay contact.


  What is the consequences?



Early failure of the contact (most benign first)
Inability to perform an open circuit due to arcing
Excessive heat due to open circuit arcing (leading to.... fire)