This entire picture is crazy. First thing, it seems to me you need to find out how your insurance processed the claim. Was is processed under Part B or Part D. Look carefully at your Explanation of Benefits and then talk with your insurer again.....ask to be transferred to someone who you can understand.

What are your deductibles? Do you have a deductible for your health plan (would include Part B benefits) and if so, what is it? You likely have a deductible for Part D, often referred to as the drug plan. What is it?

And how much of your deductible had you met when your Evenity claim was processed. Could this first Evenity payment include a very large deductible that might not be part of subsequent payment obligations.

Every Advantage plan seems to have slight differences making it very difficult to compare apples to apples when we discuss things like this on Connect.

IF you still cannot make heads or tails about how your claim was processed, consider getting help understanding how the claim was handled and what to expect next about your responsibility.

You might get this type of help from either your State Health Insurance Program https://www.shiphelp.org/ or from the Medicare Rights Center https://www.medicarerights.org/about.

By the way, who is your insurer? Do you know whether you received prior approval for the Evenity? Are your medical providers 'in-network' or 'out of network?'