Typically, try hitting "Restore Order" in settings. However, it also depends which screen you made the purchase on. If it was the screen that says "Buy & Use" then it was automatically added to the current planet that you were on. To refresh the planet, toggle between planet view, system view, and galaxy view, and back to planet view, or simply switch planets and back to refresh your planets production numbers.
If you made the purchase in the Items Store tab, then the resources were added to your inventory, in which you will need to click on "My Items" > "Resources" > "Use" in order to use the resources. Be sure you are on the correct planet before using them, as they will be added to whichever is the current planet.
If you still cannot find the resources, note down the time you made the purchase and send any screenshots or relevant info by email to firstname.lastname@example.org
. Also include your commander name and server in the email.