Why is my item not showing in Google Shopping but Google Merchant Center is showing it is inserted?
For the item that is inserted into your listings but doesn't come up when you search, that is another issue for which you should contact Google. The item is clearly inserted but somehow Google doesn't think it is optimized for that search phrase. If there is some sort of penalty Google is imposing on that item, they should let you know. Could it perhaps be the item comes up in the search but Google has ranked it very low?
The following link is one merchants use to contact Google about disapproved feeds, but you may be able to use it to contact them in general if you cannot locate the contact link in your Google Merchant Account.