Battery failure Samsung Galaxy S7

My Samsung Galaxy S7 developed battery issues after about 18 months use. With the battery level still indicating 50% battery power the phone will shut down. The phone will then be charged and only after about half a hour the phone will again shut down. I then decided to take the phone to my MTN service provider at Oakfields, Northmead, After it was taken out of it's protective cover it was discovered that body shell and screen has separated, The battery has swollen to almost twice it's size. I was advised it is a wonder that the phone did not explode. The assistant informed me to take the phone to SSS Cellular as it is still under warranty. There I was informed that it is the battery and that the warranty has expired after 12 months and that I will have to pay . I am not satisfied with this as it is a battery failure where the battery nearly exploded. This to the detriment of my safety. Why should I pay R 1 100.00 for repairs to the phone? How would I be able to trust the unit and the product again taking into account news articles on this subject?