Very bad services from vodacom and samsung

I have done a upgrade and got the Samsung S6 after 6 days i took it back as the battery is running down very fast.i had to charge the fone 5times.vodacom sent the fone away and got it back saying there's nothing wrong with the fone.I got the fone switch it on and after 2 ours the fone lost 40% battery life.I charge the fone,again after 2 ours the battery was on 70% vodacom says sorry they cant do anything about it.Samsung said they can't do anything about it. Who's to blame?I took the fone in within it's 7 day warranty and still know once taking responsibility.