Faulty Blacklisted

I am writing this on behalf of my mom, she had the worst experience with them whereby in 2020 she took her phone in because her screen had broke they took literally 7 months to fix her phone and bare in mind they where still debting money from her account every month but she did not have the phone, and when she eventually complained at cell c mall of the north they told her that her phone is "missing" and that she would get a new phone. They eventually gave her a new phone but she had to pay a excess of R3000 something than the next month they debt close to R6000 and when she asked the consultants at cell c Savannah mall they told her don't know why the company took so much money and she needs to reverse it. Recently she went and tried to make a personal loan at the bank and was told that she had been blacklisted by cell c. The next week she went to cell c mall of the north and asked one of the consultants to assist by giving a letter so that she can go a borrow money the case number was : *** and she was told to call after 3 working dats of which she did she was told they can't assist in any way and she needs to pay a whole R15000 back to them before removing her from being blacklisted.