Cellphone not working

My mother do have a blackberry curve with Cell C on a 2 year contract which of a year is completed. She went to them on numerous occasions to fix the cellphone. They took it twice for 21days to get it fixed but still she struggle with her phone. They want to take it in for another 21 days. During this past year she did not have any joy of the phone but she have to pay her monthly payment. I can't see why they can't get it fixed for once and for all or give her a new phone, every now and then she loose all her data and info.