Disgruntled customer

My wife took her Samsung Galaxy S6 Edge in for repairs last month and three weeks later the battery swells and the guy says it our fault it cost us R450, when we took the phone to him today and told him the problem he says it's our fault. We asked him to check the phone to see what the problem could be and now the phone doesn't want to work when it was still on when we took it in. I am so not impressed with the way this shop handles customer service. They still want to charge us for a new battery that was faulty to begin with