It is good that you tried the serial.
But did you check that the BV20 is configured for the correct serial settings that will match up to the Arduino, using BV20 setup software.
For example check the BV20 is set to 9600 baud.
Also, try formatting the data in your print statement as HEX, eg Serial.print(data, HEX), that way you'll see any character even if non-printable.
Also, change your Serial.println to just print, take the 'ln' off to help you see the data better if it is just characters.
If your serial window is too small, you may miss any characters that are received.
You did also connect the ground of the BV20 to your Arduino ground too?