Cell C responsible for losing money

Contract (expired) was cancelled around 21 months ago, I went over to Vodacom. 20.3.19, after nearly two years, my bank told me that I was "blacklisted" by Cell C for outstanding amount of around R500! After calling customer services, holding for the CC legal department for 45 minutes at a time, I eventually got through to a lady, that confirmed that I HAVE NEVER OWED OR STILL OWN CELL C ANY MONEY. As it is a public holiday, the next day, I should call again today, Friday, and ask for a paid up letter. Called today on several occasions, was send from one department to another, and still, the legal department number not working, they will escalate the problem, sorry and all the other nonsense they talk when they made a mistake. I app**** for a advance at my bank, and have tilers coming in on Monday, but due to CELL C, I will now have to pay them, without getting the money from the bank, as I am marked as "blacklisted" but I have never owned ANY money to CELL C, confirmed by their LEGAL DEPARTMENT. After calling around 6 times, holding for hours, now they will call me back within 48 hours, and then I could be helped. THIS IS UN ACCEPTABLE, POOR SERVICE. THEY SHOULD BE ABLE TO HELP ME IMMEDIATLY, AS IT IS THEM THAT MADE A MISTAKE. I will have to pay workers, for doing nothing, until Cell C supply the letter, and the money can be paid out by the bank. We should be able to hold Cell C responsible for paying the workers.