Why are there multiple social security numbers?

This situation is generally caused by the system information not being updated in time. For example, if you work in company A, the company pays social security and generates a social security number.

Then I went to work in company B. Because the system was not updated, company B paid social security and generated a social security number. So you have multiple social security numbers.

In this case, go to the social security bureau (some cities are local taxes) to merge social security.

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