I think you got some good helpful information to your post "Medicare Part A and B" back in July, 2017.
There seems to be several issues: the credits with Social Security and then your preferred insurance.
I see from your 2017 reply that some of your working credits seem to have been lost. This is very worrisome (to me, even though you say you are not worried). I don't recall the specific rules but I think one needs 40 credits (equal to 10 total years of work history) to be eligible to collect a Social Security benefit. I am not certain how this affects Medicare though. It is certainly something to check into...though I understand that you want no part of Medicare. But realize that this is your benefit for your years of paying the payroll tax into these plans, you have earned this and are entitled to it, it's not charity.
As to whether you can voluntarily desist from Medicare, I recall some pretty specific (and almost harsh) rules on this in my own case. I recently retired at 66 but I had to sign up for Part A when I was 65...otherwise there was some penalty (I do not like penalties in the form of $$$, haha). Of course, there is no cost involved in the Part A. When I did retire I went to Medicare Part B
The premiums for Medicare Part B are very small compared to what we must pay for my wife's health insurance under the ACA ("Obamacare" if you must, though I do not like that name). Of course, it is now the law of the land that one must have health care (if not on Medicare), either through employer, through ACA, Medicaid, etc. If ones income is sufficiently high then they get penalized on federal income taxes if they do not have creditable health care.
Now you could get your own policy from United but I imagine the premiums will be pretty high.
As suggested in the replies to your post last year it seems that you really need to discuss these several issues with someone in-person locally. There is a lot of background to be filled in. You might get this information from a local AARP office, from the local Social Security office, from a local health care (ACA) guide (they offer such services at no fee). Or from a local church or other such group.
Good luck!