Worst service samsung

Hi I took out a contract at Vodacom a51 Samsung I got the phone and it had issues freezing overheating with minimal use I then went back to Vodacom within 7days and told them I would like it replaced they said it was a obf they will send it away and my phone would me replaced with in 5days I then waited 12days eventually I got the same phone as the obf was rejected I fetched the phone which is even worst now don't know what **** the tech guys did as the camera is blurry and not as bright as it was everywhere u can take a phone back with in 7days if not satisfied it will be replaced what the hell is your guys problem I want my phone replaced I'm not paying for this second hand problematic phone. phoned and emailed Samsung still waiting worst customer service Samsung please let someone that has authority to contact me not useless call centre agents