Changing I2C_ADDR to 0x20 has no effect.
Don't just change it: read the datasheet and see what it is.
There are two notations for i2c addresses: somepeople use the 7-bit convention and others the 8-bit convention. so an address of 0b010 0111 (0x27 in 7-bit convention) can be represented at 0b0100 1110 (=0x2e in 8-bit land, and that's actually how it is sent to the device).
So when you see an i2c address of 0x27, you need really to see the bit pattern to be sure.