Billing

I have paid up my account in December 2017. I went to the store, stood in front of the cashier, she handed me the phone and told me to inquire the amount to settle and close my account. The amount was given and I paid it in full. I did it at the store because their online services and contact numbers are pathetic. I got an sms today saying I owe an additional R100 some odd which just came out of the blue. I spoke to someone on chat who gave me the complaints number, which does not work. I am disgusted with this company. I was assured my account is paid up and closed as I wanted nothing more to do with them, only to get an sms 2 months later. They really need to be shut down and investigated. This is *****