When I attack on rebel camp I get very less gold and at bottom showing some note which says-->"Depot..

This may be a bug in the game. The message is possible to get when gaining resources from attacking monsters and other players. Each resource will have a limit that you can store based on the level of your depot buildings. Each resource has its own storage building (eg Food storage). You need to upgrade these to increase the cap.

Gold doesn't have a storage limit though. You should be able to collect it. You can check to see if you do get awarded the gold as you should when this happens as it may just be a bugged message.