There's the other issue of the notice itself. If they decided in March to make the change, how much time did they give customers to decide? Given the timeline, it seems like it was "effective immediately" rather than giving proper ahead of time notice.

Nonetheless, even if they did discuss refunding, the entire process seems shifty. Every service I use (I checked!) warns me five business days in advance by email that they are charging my card or sends a physical mail two weeks in advance. Instacart should be sending an email on each event with the delivery fee spelled out clearly.