. . . . it seems I was updated to 2020 edition for free. Is this the case? . . . .
If you are using the Plus or Premium version and your annual Update Service subscription is active then as each new release (not a patch) comes out you will be upgraded.
. . . . purchased the 2017 edition and the 2019 edition in the name of upgrading . . . .
As you purchased the 2019 version you must still be within the subscription period
Do note that, currently, upgrades are in effect a new installation and you do need to download and install all your purchased content again.