What's the use of social security card?

The social security office does not renew the card. As long as you transfer from the original unit, the new unit can insure you. The purpose of renewing the card is to prove how many years you have paid social security fees, which may be used when you get a pension at retirement age. Just keep it for yourself.

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