Apparently, I am in arrears

I received a text, well, via my Mum since I no longer am in SA. The text says that I am in arrears. Bear in mind that my December statement does not reflect this. I received a DEMAND, demanding their arrears money within two days?! Clearly they do not know what they are doing. I sent Cell C a message on Facebook, only to receive a message saying, ‘ You owe us money’. If so, where is my arrears statement? And since when are companies by law allowed to DEMAND money within two days?! I am disgusted and disappointed in their service. I am still awaiting my statement from them. I sincerely hope they get their act together! Their legal team surely should keep up to date with the law!