swollen battery

I am a Vodacom customer and I feel that it's wrong that I have a samsung s4 and it's not even a year old. phoned them to tell them I have a problem with my battery being swollen and my phone dying all the time. They said that they would fix it. I told them my phone is still under a contract. They didn't care. I phoned Samsung who told me I can come in and buy another one for R500. I think that is unacceptable I have never had an issue with swollen batteries before and I know they have replaced people's batteries before free of charge. I want to know why I have to pay if the battery is not even a year old. They said my serial number was wrong and my battery wasn't in the bad batch. Well I hate to in for you but when a battery is swollen before a year is up you have a problem. I can't believe how much these people want to make money off you. I pay a lot for this phone as it is still under contract.