Very sad.
My apple snails are no more.
In fact, they never were: they never came out of their shells in my tank.
Apparently – having called the aquarium I bought them from – some areas of my town have increased copper in their water due to the drought. And this kills snails, like, instantly.
Was there a mention of this at the shop? No. Was there any suggestion that there might be an issue? No. And how does the shop know about the copper? Because they had a batch of snails drop like flies a few months ago, got their water tested and found out about the copper. So this is not exactly a surprise to them.
Argh!! I sent a moderately-worded email expressing my disappointment.
No snails, again! I’m so sad. And one of my lovely new cloaches died, too. But the other three seem happy enough….
Randomly Yours, Alex 
By law this would be a unilateral mistake and the aquaria can/and should correct this as it is of their fault (on accident)
I did wonder whether they would take any responsibility. It will be interesting to see whether they reply to my email. Unfortunately, they’re the closest aquarium to us – to get to any other one is something like a half hour drive.