Disability & medicare

I’m disabled & have been on disability since 2005 (have MS). I was always covered thru my husbande’s ins. through his job. In 2007, I rec.,w/o asking for it, a medicare part A card. I didn’t need it, so I just put it in my wallet & didn’t think about it again until…My husband, Greg lost his job approx. 20mths ago. He & I went on Cobra and pd a fortune for it. Things are going from bad to wors. Medicare says Cobra isn’t “credible” ins., but won’t give me a reason. Soc. Sec. is threating to fine me. I can’t get on Medicare until GEP. They won’t say why. By the way, my husb. had a stroke 1-4-19 & is now totally disable & on disability. He can’t get on Medicare until he’s been on disability for 2 yrs. Why that long? They won’t say why about that either. Were now on marketplace ins & paying a fortune for that too (sorry for the typos but I’m a lousy typist).I don’t know where to go and try to get help. PLEASE offer help. Thank you