It is possible that your ad is not visible on the page. You can go to your profile and then click on my listings. You should be able to see the ad there.
 
However, if you don’t see the ad on the product or category page. It is possible that your ad has become old and hence has gone to the later pages. This usually happens when news ads come in. The older ones get shifted back.
 
You can also go to the search tab and find the ad there. Ads expire after 90 days.