We just went through this. DW became eligible for Medicare. Healthcare.gov has an option to make changes in status. Unfortunately, I couldn't get it to work right so I called the help line. I was on hold for a few minutes, but not really long. After I explained the situation, the customer service rep made the changes we needed while I was on the phone with him. I checked online later and everything looked good. A few days later, we got a letter from our ACA carrier, Blue Cross of Florida, that they had received the change. I contacted the Healthcare.gov help line about 2 months before the changes were supposed to take place. I was surprised at how easy it was. Billing was direct debit and the amount was automatically changed to reflect the new situation. Of course, your mileage may vary.