Dangerous batteries quality, please do not use it for i phones

I got my battery replaced for i phone 6 on 3rd march 2018. almost after six months issues with the battery started. my phone would show 80% charged and the next second the phone was dead. I thought may it's the new ios upgrade or any other app that i downloaded but in 2 to 3 days the phone battery just worsen and I had to frequently change my phone. I decided to use another phone and when I wanted to take the sim out of the phone I noticed that my phone is damaged due to the swollen battery. It was almost as if it was about to explode. I wanted to give the phone to i store but they wouldn't service my phone as my phone was opened by some other vendor. I took my phone again to Wefix woodmead and they told me that I overcharged my phone and it's out of warranty period. I showed them my another i phone 6s which was in the perfect conditions with my same s****s of charging the phone. They wanted me to pay another R450.00 to put back the same **** in my phone. The batteries that they put in i phones is dangerous and can blow up the phone. I will be putting the pictures of the damaged phone on to social media so that no one buy such ****py product