WONGA IS RUINING MY CREDIT SCORE ON PURPOSE

Even though I had settled my account in July, they still refused to close it. Instead they keep it open and worse trying to charge me interest on a 0 balance account (its literally at R214 right now!!). Even though they sent me an email and SMS stating it was settled as well as the statement shows it was paid in full, they still refuse to send me a settlement letter (instead they sent me some generic email about how it will be solved, THAT WAS 2 MONTHS AGO!!!) and the worse part is that its affecting my credit score as Credit Bureaus think I owe them over R7500!!!! THIS IS RIDICULOUS!