The 90-day doctor visit requirement is part of Medicare Part B that covers insulin pumps, insulin, pump supplies, and test strips. Here’s a comment that @Laddie posted on this topic in 2016.
This is from my comment on the same thread. I followed Laddie’s Medicare National Determination Letters link and cut and pasted the pertinent section.
Continued coverage of the insulin pump [and related supplies including insulin] would require that the patient be seen and evaluated by the treating physician at least every 3 months.