Cell C complaint

In 2016, Cell C offered me a contract phone, we are agreed on J7 cellphone model, they delivered the phone to me via courier, when I opened the box, I found out that it is not the cellphone we agreed on, I immediately called them to take their cellphone back, they came, took the phone, now I have been trying to buy a car, but all the banks declined, I then went to check my credit profile, I found that I am owing Cell C, I went to the store to check how so, at the store I was told that I am not owing them, they advised me to contact their legal department, I have been trying to call them but the phones are not answered, its been weeks now trying to get hold of them, please help me with anything you can help me with, my life is stalked because no one is willing to give me a credit because of what Cell C is doing to me.