Nobody stole anything. A player took items from a source he was allowed to take from. Now, it might be one of your FC's rules to not take everything from the chest, so you have every right to remove him from your FC, but those items are his. This is something that could have been avoided completely with rank restrictions. If you as an FC leader only want players to get a certain amount of items a day, then you should only make a certain amount available a day. SE has no responsibility to fix this for you, and in fact it wouldn't be fair since they've refused to do it in the past.

This whole thing could have been prevented by a small amount of foresight and a very tiny bit of effort.