I can understand a request to call and acknowledge receipt, but nothing more.
I am on Medicare because of age, not willingly. Last year, I changed carriers to one domiciled in Ohio. Immediately, I started getting calls to complete an extensive health questionnaire and robo calls. That new carrier apparently had a lot of "business associates." Most Americans don't realize that the HIPPA act (a law that basically codifies health information privacy) covers doctors, hospitals, and others but largely exempts insurance companies for "legitimate business reasons." In reality, healthcare providers were asleep and insurance companies had powerful lobbyists working while it was debated in Congress. Initially, the impact on medical care was significant. As an example, a hospital-based physician such as a pathologist or radiologist might need to get a patient's consent to review the medical record in order to do work sent to them for a diagnosis. Distinctly different was sharing information by insurance companies. That early situation has been dealt with reasonably well by modifying patient consent forms. Patients may still get what seem like needless requests to release information by some providers.
On the subject of providing individual health information to "help us improve our services," for Medicare and Medicaid beneficiaries, I don't believe you are required to do that. In the personal instance mentioned, I have provided nothing. The carrier and its contractors have continued to send/call me for follow ups, but nothing adverse has happened.
For private insurance, if the premiums are risk-adjusted, you may be required to provide that information.
For employer-provided insurance, I believe you are not required to answer a health questionnaire, but I am not sure.* It may depend on the size of the employer and/or whether employees are unionized. I agree with what you did. If CIGNA persists, you might need to get more current advice.
*EDIT: During my employed years, I never had to provide that information. But then, my "insurance" was provided by my employer who was also my healthcare provider.