When you're supporting and your team feeds but then doesn't surrender and just farms

You also farm. If they rage at you for taking farm, tell them to surrender or play better.

You win.

ward so that they're safe while they farm, assuming they bother to watch the minimap.

You endure it.

Quit LoL.

if you are angry that your team is trying to win despite being at a disadvantage, a game that you will lose half of the time despite your best efforts is not a game you should be playing.

You play the game... If you're behind why do you want to fight? Farm up and win team fight engagements when you aren't at such a disadvantage.