Vodacom repair centre cheats

I got a brand new phone from vodacom@reds, took the phone back because the battery doesn't last and phone gets hot, repair centre said there is nothing wrong with the phone. Now the phone is still getting hot and when i plug the phone out after it is fully charged the drops power immediately and the battery just keeps dropping overnight without being used, it drops from 100% to 60% in three hours, so how did the repair centre test that, when my old phone used to keep the battery power when not in use