Is it illegal to pay social security accumulation fund?

This practice is illegal in itself, and it is even more illegal if it is stipulated in the form of peers. It should be said that this kind of contract that conflicts with national laws is invalid.

You are willing to apply to the district-level labor arbitration committee where your unit is located for arbitration, and propose to pay social security in accordance with the provisions of the Social Labor Security Law and the proportion of individuals and units.

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