How does the company inquire about employee social security cards?

If you are in Shenzhen, you can check with the Social Security Bureau. If the company issues a certificate, you can go to the Social Security Bureau to print out a detailed list of previous payments.

If the company doesn't want to check it for you, you can go to the Municipal Social Security Bureau and print it with your ID card and social security card!

Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.