MassHealth is what the state of Massachusetts calls its Medicaid program. Once a person, in any state, becomes eligible for Medicare, then Medicaid becomes their insurer of second resort. It will cover what Medicare does not cover. Medicare is the insurer of first resort. Medicaid recipients - in any state - are expected to take full advantage of their Medicare eligibility.

I think what the reps are trying to tell you is that you lose access to MassHealth when you become eligible for Medicare Part B, but fail to enroll in it. They know you are eligible for it because they know you have Medicare Part A. (Being eligible for Part A implies that you are also eligible for Part B.)

Your state expects you to enroll in Medicare Part B, in order for you to continue getting the additional help from Massachusetts Medicaid. The good news is that the State of Massachusetts will pay your Part B premium for you. You qualify for that because your income is low enough for you to qualify for MassHealth. Here is my source for that: What if I cannot afford Medicare? - MassLegalHelp

An excerpt:

If you get MassHealth, it will pay your Part B premium and your Medicare prescription drug coverage, Medicare Part D. You may also be able to get help paying out-of-pocket co-payments to doctors and hospitals.

To get this benefit, you have to enroll in Medicare Part B and initially pay the Part B premium yourself. (It will be deducted out of your Social Security check.) Then you notify your Income Support office that you need help paying the Part B premium. Getting that premium paid by the state, on your behalf, is part of what Medicaid in your state will do for you. It's part of your MassHealth benefit. Eventually, the State of Massachusetts will reimburse you for the initial Part B premiums that you pay while you are waiting for the benefit to kick in. They will pay the Social Security Program who will then apply a credit to your Social Security payments. You'll get the money back in the form of a payment from Social Security, in one or two lump sums.

I do not live in Massachusetts. (I have lots of relatives who do.) I feel confident of what I've just told you because no state is more generous than Massachusetts. My Medicare Part B premium is paid by Medicaid in my state. If your income is low enough for you to qualify for Medicaid in MA, then your state of Massachusetts will do the same thing.

You kind of shot yourself in the foot by not enrolling in Medicare Part B when you initially became eligible. Because you held back from doing that, you will now be charged a sonewhat higher premium to get Part B coverage. That is a penalty, some of which you may have to pay out of you own pocket. That penalty is going to get bigger every year that you hang back. Here is a source:

https://www.cms.gov/Medicare/Medicar...fo/Part-B.html

An excerpt:

Caution: If the beneficiary didn't take Part B when they were first eligible, the cost of Part B will go up 10% for each full 12-month period that they could have had Part B but didn't sign up for it, except in special cases. They will have to pay this penalty as long as they have Part B.

Do yourself a favor. Enroll in Medicare Part B the next time that enrollment is open to do that. It sounds like you've been trying to finesse the system to save money. The result is that you have no coverage for doctor bills . . . and other things. What you're doing is hurting you.

Once you enroll in Part B, then, if your income is low enough, you will have full Medicare and full Medicaid. When you are fully covered by Medicare and MassHealth, which is Medicaid, then you will be eligible to enroll in Care One, which is your state's program to blend your Medicare and Medicaid coverage into one program that will save you even more money.

You are using the term "MassHealth Care Plus," which is a fuzzy term that I don't think really describes what you have. I think that may have been supplanted by current programs.