Yes I have, and it's not unusual for the new insurance company to question why an SCLS patient really needs to receive IVIG and why every 4 weeks -- including when that new insurance company is Medicare.
Therefore, you may have to submit to them copies of your prior insurance company's records showing that they covered your infusions, and supplement that with an explanatory letter from your main doctor, and also copies of, or links to, articles appearing in the Disorder Resources section of this website -- and particularly the latest article by Dr. Druey and team from NIH, see the Discussion Forum topic "Publication of Results from Survey of IVIG Therapy."
The good news is, unlike when some of us pioneers went on IVIG years ago on an experimental basis, now there is abundant evidence that IVIG is the most effective treatment for those duly diagnosed with SCLS and with a history of recurrent episodes which were not prevented by other, cheaper medications.