Quick to sell quicker to blacklist ZERO DONT KNOW WHY themselves reason

Please assist. I am getting threatening letters from HP Pole Attorneys (from Cell C) which will not tell me what the bill is for yet I better pay or I will be listed. I ask for a statement for over 5 months and all they send is that I owe? They dont say for what. They say cellC just loves to hand me over with no description of what the amount is based on. I took a 24 month contract/paid 24 payments/sent a statement with 24 payments but they want extra 2months??? Who can i get help from? Regards Gregg