How Do You Deal With Fed Assassins as a Squishy Champ

Because it seems like every game I'm forced to just accept that fact that no matter where I am on the map, even in my own base, I can get 1 second bursted. I've had fed assassins run through turrets into my base just to kill me. I can't farm I can't go in the jungle the only safe place is in fountain. I play mostly support, my second played role is adc. The only thing I've had somewhat work, is play Yuumi and the second an assassin appears on my binded partner I spam my heal and hope the heal and Athene's is enough to save them. It seems like there really is no counter once they are fed. There really isn't anywhere you can go that is safe. They can get into base, behind your frontline, there is nowhere you can safely farm if you have to. Traveling with a teammate is pointless because you are bursted down before your friend can press a key. I'm legit asking, what can you do in this situation. They make the game so unfun to play.
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