Cell c it's a ****,threatening to blacklist me

Cell c it's a ****,during the month of December,they decided to make a debit order from my account without informing me and there was no money in my account and it was nt our agreement date,since from then they started claiming that I owe R75,00 more for late payment,I lodge a complain via email,while they were still doing their investigation i was paying via eft to avoid being in errears,the matter was resolved in March as per case number *** and it was on the 8th of March,the same thing happened again in April they added R75,00 on my instalment I send them emails with no assistance,I paid via eft and money kept on accumulating in may they blocked my SIM card (data) and kept on adding money,they keep on saying I should pay regardless I'm nt getting any service from them or they will blacklist me,I stopped paying from may since the SIM card is blocked,your assistance will be highly appreciated