Uncaptured payment and threats of blacklist

I am having a huge problem with Cell C and it is getting worse every day. On the 5th of October 2015 I made a payment of R100 in advance for my cellphone contract. The transaction was made through Standard Bank cellphone banking and the reference number was automatically made by the system. As per procedure, I sent the proof of payment to the relevant Cell C email address. I sent the first proof of payment for the same transaction on the 26th of October 2015 but until this day that payment has never been captured. Ever since then, they always threaten me by suspending my line during month ends and further telling me that they will blacklist me or put my name on the list of people with bad credit history. I have been sending them the proof of that payment more than three times every month and until this day it has not been captured. I call their call centres to see if it has been captured but they keep asking me to resend it and wait for two days while they keep threatening me buy subsequently blocking my line and telling me to pay them the R57.22 which I owe them, that amount was supposed to be covered by that R100. I am tired of being the victim of being threated. Please help....