WORST SERVICE, I WANT MY PAID-UP LETTER CELL C

I paid up my contract with Cell C last year and they advised me that they have taken me out of their system, to my Suprise I am now getting calls, SMS's and emails from MBD threatening me that they are handing me over to their lawyers when I have already paid the account of cell c and when I call cell c for the paid up letter so that I can sent it to MBD so that they can take me out of their system they told me I will get the paid up letter in 248hrs and its been 4 days today and I have not received my paid up letter from cell c and I am going to be blacklisted coz of their incomitance. My case number is ***