Accelerometer SA0 & SA1 Pin hanging
According to page 18 of the datasheet:



If the SA0 pin is left floating as you have done, the chip will run in SPI mode. However the CS pin is multiplexed with SA1 which you have also left floating.

As a result there is no way to talk to the chip. You can't use I2C because you have set it to SPI mode, and you can't use SPI because you've left one of the SPI pins unconnected. Because it is a QFN chip you will find it very difficult if not impossible to correct. You might just be able to solder magnet wire (thin wires), but that will be tricky.

Your best bet is to redesign/remake your board. Remember to always double and triple check your schematic and compare it with datasheets.