Try moving the chip to a fresh new location on your bread board.
Also, measure individual pins to check they are getting all the right voltages.
Also, make sure you have 2 power decoupling caps right on the power pins to GND.
Also, maybe show us a simple schematic of your wiring.
Also, what evidence do you have that your IC isn't a Chinese clone.
And, lastly, what kind and value of caps are you using for cextA and cextB.