Different programs
Medicare is federal health insurance primarily for people 65+ and certain people with disabilities. Medicaid is a joint federal-state program based mainly on income and other eligibility rules. They are not interchangeable.
Dual eligibility
People with both Medicare and Medicaid are often called dual eligible. Depending on the exact level of Medicaid, they may qualify for Dual Special Needs Plans (D-SNPs) or other assistance. Benefits vary by plan and county.
California note
In California, Medicaid is called Medi-Cal. Coordination rules, D-SNP availability, and Medi-Cal managed care can be specific to your county. A licensed California agent can help you understand the landscape — not promise a particular plan.