Settlement of my account and Wrong installment reflection

I am extremely dissatisfied with Vodacom's handling of my account. I settled my account in November, with a monthly installment of R250. However, my credit report falsely shows that I owe R1,500, as if my installment was R1,250. This is completely incorrect and has severely damaged my credit score. Despite being told my account would switch to prepaid, I never received a settlement letter or any written confirmation that the account was closed. I am now struggling to dispute the incorrect credit reflection and cannot get help from Vodacom. I demand an immediate resolution, a settlement letter, and correction of my credit report.