Abolish the penalty clause & open enrollment time-frame for Medicare part "D". I am being discriminated, I need to elab.

I am 68 yrs. old & still working, I signed up for Med. part "A" but not any other parts as I was working & did not need them, now I do I am a diabetic and need my insulin & meds. I applied for part "D" when my co. medical ceased, I applied well within the 63 day limitation but now it seems that Medicare wants to charge me a penalty, for what? because I saved Medicare money for the last 3 yrs. by not being a burden.