MTN and Truworths are together, BAD

I bought my grand daughter a phone, Nokia Lumnia in 2014, it was not working within 3 months. She took it to Truworths in Auckland park, they didn't have cell phones so they sent her to MTN. MTN took the phone for repairs, brought it back in a worse condition, it couldn't charge. She took it back to MTN, they took it back for repairs and wrote a report that it's physical damage. my Question is what kind of physical damage and they claim that she opened it which she didn't , MTN were the first people to open that phone. They then told her to take it back to truworths where she got it. The phone is still at truworths, I'm getting no help. I took the matter to consumer affairs but I'm not being helped there also. They keep on calling that I must pay my account, how can I pay for a phone that is at the store, not working. The manager from Truworths is not helping at all. I've complained to truworths head office, a lady called me, I thought she was going to help, she understood but now quiet. A lady from MTN called and said she wont even meet with me, she was very rude. MTN were the first people to open that phone, now it's our fault?