I think you are wrong. From what I've heard (and don't quote me) is that at some point plan F for NEW subscribers will be going away. If you currently have Plan F you can keep it, and I think you can even change carriers.
Both dh and I have Plan F and use different companies for our supplemental plan. We also have Plan D. We are keeping Plan F and D. I am in the process of changing carriers this year and dh will probably do so as well.
From information found online at medicare.com. Here is link to entire article:
https://medicare.com/medicare-supplement/is-medicare-supplement-plan-f-going-away/
Is Medicare Supplement Plan F being discontinued?
The Medicare Access and CHIP Reauthorization Act of 2015 (MACRA) passed by Congress and signed into law on April 16, 2015 changed the law on various aspects of health care, including some Medicare Supplement plans. The new law states that on or after January 1, 2020, a Medicare Supplement policy that provides coverage of the Part B deductible may not be sold or issued to a newly eligible Medicare beneficiary. You can read more
here. That means that people whose birthday is December 31, 1954 (turning 65 on December 31, 2019) may be the last group able to enroll in Medicare Supplement Plan F. After January 1, 2020, you will not be able to enroll in Medicare Supplement Plan C, one of the closest alternatives to Plan F, either, since it also covers the Part B deductible.
If you already have Plan F, you can keep it. The law only affects new enrollees.