I don't see that you have any valid complaint. You say yourself that closing at 10 means closing at 10. That means no more shopping, not just that the front door is closing. You had plenty of warning, and you have no right to keep shopping after the posted business hours. Granted, you may have gotten attitude when you walked in, but it's actions like those you then did that lead to such attitudes.

Do you really expect a manager to know the prices of all the MANY products a Walmart carries? I sure wouldn't be able to keep them all in my mind.

I really don't think you taught anyone there anything about how to treat customers, including class and respect.