First, contact your doctor.
Explain to your doctor that your Part D plan refused to cover your drug
because the prescribed dosage is not on the plan's formulary. Find out whether
your doctor will prescribe a substitute drug or a different dosage that
is on your Part D plan's formulary.
If your doctor believes that you must have the prescribed dosage, then ask
your doctor to contact your Part D plan to request an "Exception"
and to explain why the dosage is medically necessary.