Such a bad service provider, that csn ruin your credit record

I will never use cell c ever again. The service i received from them regarding my contract was so bad. I told them i didn't want to upgrade my contract anymore, 3 days later my sim card was block by them with my data, airtime nd mins, they told me that if i dont upgrade they have to block the sim that i was using. After that they ruined my credit record says thst i owe them money after 5 months not hearing from them, what even makes me mad is that 3 months back i called asking them to check for me if i still owe them nd they said to me everything is cleared out, i then asked why does it shows on my clearscors, she told me not yo worry it takes time on them to clear out. But now i receiving calls, i am harrased by their lawyers saying i owe them. Mxm