Financial questions that need an answer

One of my manufacurers is selling the same items it sells me to a larger corporation that doesn’t match my income however they are giving them a lot better price for their items I have sent emails asking why this is so but they won’t reply. What should I do should I cut them off or just roll with it.
Like I mentioned I sell a greater volume than they do thats why I can’t understand the pricing difference and the company I speak of getting the better prices is wal-mart.