Conclusion
Medicare Advantage Disenrollment Period (MADP) is a period when people covered by Medicare Advantage Plan can cancel their plan and move to another plan or an original Medicare. To cancel your plan, you have to contact your plan provider through a request letter stating everything you need.
References;
[1] https://www.ssa.gov/benefits/medicare/
[2] https://www.healthcare.gov/medicaid-chip/getting-medicaid-chip/
[3] https://www.insurance.wa.gov/what-medigap-plan-and-why-should-i-buy-it
[4] https://www.humana.com/medicare/part-d-drug-plans
[5] https://www.ncoa.org/article/understanding-medicare-s-late-enrollment-penalties
[6] https://www.medicare.gov/sign-upchange-plans/types-of-medicare-health-plans/medicare-advantage-plans