Refund

I bought a huawei p20 lite cell phone at Vodacom Canal Walk on Saturday the 28th and the phone was switched on by the consultant and she told me that if I experience a fault with the phone in the following 7 days then I should bring it back to them and they will give me a new phone. well the phone ran out of the battery Saturday night then I charged it until it was full, Sunday morning that phone was 100% full but by 13:00 battery was 68% and I didn't leave any apps running and by 16:00 it was on 42%, and this morning it was 10% and I didn't really use the phone that much, I even called huawei client services to explain to me what could be wrong and which things must I switch of but that didn't work.When I took it back to canal walk I was told that I must wait for days so that they sent it to get checked out while the consultant told me that in the 7 days I will get a new one but it turns out that its not that way and I asked for my money back but the manager refused to give my money back,

WHAT DO I DO WITH THIS KINDA SITUATION?? please assist