The company buys us social security, only medical care and work-related injuries, but no old-age insurance. Is it legal? What if it's illegal?

Employers should pay social insurance in full for employees, not just work-related injury and medical insurance.

If the employer's behavior is illegal, the employee may apply for labor arbitration.

Article 72 The sources of social insurance funds shall be determined according to the types of insurance, and social pooling shall be gradually implemented. Employers and workers must participate in social insurance and pay social insurance premiums according to law.

Article 73 stipulates that social insurance benefits enjoyed by laborers must be paid in full and on time.

Article 100 If an employer fails to pay social insurance premiums without reason, the labor administrative department shall order it to pay within a time limit. If it fails to pay within the time limit, it may impose a late fee.

"Social Insurance Law" Article 64 Social insurance funds include basic old-age insurance funds, basic medical insurance funds, industrial injury insurance funds, unemployment insurance funds and maternity insurance funds. All social insurance funds shall be accounted for according to the types of social insurance, and a unified national accounting system shall be implemented.

The social insurance fund is earmarked for special purposes, and no organization or individual may occupy or misappropriate it.

The basic old-age insurance fund will gradually implement national overall planning, and other social insurance funds will gradually implement provincial overall planning. The specific time and steps shall be stipulated by the State Council.

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