Okay, they changed the policy. Companies do that all the time and as much as we don't like it, most often they need to so they can either continue to be profitable or just to continue providing their service. This seems like such a case. (Imagine Instacart's yearly customers ordering a banana from the grocery store and not paying any shipping fee - this was probably done to prevent abuse).It's disappointing but not out of line.
They sent out a notice. One person and their two friends didn't get the memo. That's truly unfortunate but then to wonder out loud if an email ever got sent out at all is another point against the author. The insinuation is that the company is lying.
This genre of blog post has gotten out of hand. It was once reserved for truly egregious acts. Now every time someone falls into an obvious edge-case they blow the whole thing out of proportion.
The bottom line here is that the company had to change their policy, they sent out notice of that and the author is framing them as the bad guys because he didn't get the memo. It's okay and understandable to be disappointed by being charged for something you thought you wouldn't be charged for but nothing underhanded happened here so it's not alright to frame Instacart as the villain.