On your main country page there is a button "automation" where you can deactivate "Buy ammunition and supplies for the army."
Probably you gave up selling orders for weapons and ammo, but the automation system already ordered ammo for weapons not sold yet. Plus if you have still active military units, your country will auto order ammo and supplies. You have to dismantle them first if you want to get rid of them.
Orders still pending can be cancelled on the trade overview page (Topdown menu at the top > Trade > Trade overview).
It also can come in handy if you mention your country +planet so we can look your country up if needed.