Selective pressures have allowed health insurance companies in the US to be as brutally shitty as possible without explicitly going door to door and kicking people in the leg. If you pay a bill it cancels the automatic payment you have set up. They notify you by sending a letter in the mail in an envelope that looks like all of their other junk mail. If you add a card for auto pay after making a manual payment and the manual payment clears before the auto, the auto pay is cancelled.