Hi:
Many stores have a sign near the doors or the Customer (Dis)Service counter.
If this is for a complaint, generally you should contact the manager first, then then owner/dealer, then Head Office. Many customers report that Customer Service just refers them back to the owner and/or manager anyway, meaning you are out of luck.
Supposedly HO keeps statistics about the number of complaints, so your situation might not even be reviewed (but instead added to some total on a spread-sheet).
You can also complain to your local Better Business Bureau, your provincial Consumer Ministry and the federal Competition Bureau.
You can also take your story to the local media, although they might be concerned about a small amount of money for one person. Some newspapers have consumer reporters, who will 'go to bat' for you, such as Ellen Roseman at the Toronto Star.
If the dollar amount is large, you can consider a lawsuit. Filing typically costs around $50, and you can represent yourself to save costs.
There are many stories where the store settled out-of-court, just to avoid having their misdeeds on the public record.
Good luck with your situation!