OMG I about cried after seeing that pic. Poor little guys! And how the employee just blew you off, ridiculous! If it was any other animal (bird, gpig, etc) people would be furious!
I would post this on their FB as well, gets the message across to other people that this is NOT okay, and IMO makes Petco more prone to doing something.
I recently recieved terrible customer service (not from Petco, another store) when I mentioned a betta vase needed more water (had about 2 cups, about 1/4 full). The employee argued with me so I called the customer complaint hotline and posted to their FB, guess what...2 hours later ALL the fish had new water.