As people across the country receive new, safer Medicare cards in the mail, advocates are warning about fraudulent callers who try to dupe people into paying money or divulging personal information.

The government is gradually replacing Medicare cards for the 60 million people covered by the federal health plan. Previously, the cards used the recipient’s Social Security number as his or her Medicare number, which posed a risk of identity theft. Congress mandated a change in 2015.

“It took a very long time, but it’s in the works,” Sue Greeno of the nonprofit Center for Medicare Advocacy said.

The new cards use an 11-character Medicare identifier that contains both numbers and letters, according to the Center for Medicare and Medicaid Services, the agency that runs Medicare.

While the cards are safer, criminals are always alert to new ways of scamming people, said Amy Nofziger, a fraud expert with AARP. Recent calls to the group’s fraud help line indicate that some people have received calls asking for a fee in order to deliver a new Medicare card, or asking for personal information before a new card can be issued.

Such calls are bogus. “The card is free,” Nofziger said, and will be mailed automatically.

According to the Center for Medicare and Medicaid Services, “Medicare will never call you uninvited and ask you to give us personal or private information to get your new Medicare number and card.”

Suspicious calls can be reported by calling 1-800-MEDICARE (1-800-633-4227), the agency said. Consumers can also call their local Senior Medicare Patrol, a federally funded service for people on Medicare and their families.

The government began mailing the cards this spring. But because mailings are staggered in 10 “waves,” people shouldn’t be alarmed if a friend or a relative in a different state receives a new card first, Medicare administrators said. The agency is about halfway through its mailings and, in “Wave 5,” recently began sending cards to people in Alabama, Florida, Georgia, North Carolina and South Carolina. Mailings to New York, New Jersey, Connecticut and the rest of New England began in July.

You can check a special section of the Medicare.gov website to see where cards have been mailed, and you can enter your email to be notified when mailings begin in your state.

Here are some questions and answers about the new Medicare cards:

Q. The Medicare website says new cards were mailed to my state, but I don’t have mine yet. What should I do?

A. It takes time for the cards in each wave to be mailed, the Center for Medicare and Medicaid Services said. The agency suggests checking your MyMedicare.gov account to see if one was mailed. (You’ll need to establish an account if you don’t have one.) If it was mailed, you can print a new official card. Or call 1-800-MEDICARE to see if your information, like your mailing address, needs to be updated.

It’s a good idea to check that the Social Security Administration has your current mailing address, since that’s the one Medicare uses, said Paul Stephens, director of policy and advocacy at the Privacy Rights Clearinghouse. He recommends doing so by creating an online “my Social Security account” if you haven’t already. Or call Social Security at 1-800-772-1213.

Everyone on Medicare should have a new card by April. But to allow for a transition period, doctors can accept the old cards until Dec. 31, 2019, the services agency said.

Q. What should I do with my old Medicare card?

A. Once you receive the new card, you can start taking it to your doctor visits and destroy your old card, the agency advises. Nofziger of AARP recommends using a “confetti” shredder to destroy the old card.

Q. What if I am signing up for Medicare for the first time?

A. New enrollees will receive cards with the new, unique Medicare numbers.