ClickBank tracks sales by placing a "cookie" on the visitor's browser. They give sales credit to the first affiliate that puts a cookie on someone's browser.
Why? The logic is that the first affiliate or referrer who sent the shopper to the page deserves the commission as they introduced that shopper to the product. It is a logical way to do it.
If you bought something through your CBmall but did not receive credit, you probably already had a cookie for that product on your browser. If you ever visited that product before, that's where you got the cookie.
To be fair, that other person does deserve the commission, don't they?
In the future, a good idea is to clear out your browser cookies before you shop in your CBmall. That will ensure that your own cookie goes on your browser and YOU will earn the commission on your own sale.
What can I do about this sale that I didn't get commission on?
Well, you could ask for a refund. Clean out your cookies. Then buy it again. But it will be painfully obvious to the merchant exactly what you did. (Not a great way to build a good reputation online)
And it isn't fair to either the merchant or the person who originally referred you. So I recommend that you leave this sale alone. Next time you want to buy a ClickBank product, go to your own CBmall, use the search engine, and buy it from there.
P.S. CBmall also installs a cookie on your visitor's machines that includes your ClickBank ID. Unlike the ClickBank cookie that lasts for 60 days, CBmall's lasts for a year. So someone who visits the mall through your link might just type in "cbmall.com" 12 months from now and your ID would still be credited.