TUSB320HAI: ESD ability for CC1(pin1) and CC2(pin2)

Hi Team,

My customer using TUSB320HAI and they encounter the ESD issues on CC1 and CC2.  They would like to pass ESD conditions are contact ±6kV , air ±15kV  that is their customer criteria also. However, they did the 3 approaches on the CC1 and CC2 but still got the failure on +4KV.Note: 3 approaches they did as the following:

5. Adding varistor (5.5V,10pF, TVM0G5R5M100R)
6. Adding 5V TVS
7. Adding a resistor(9.1ohm) in series.

Could you kindly provide what the ESD components or other suggestion that can improve ESD ability on CC1 and CC2.