I joined RAIN, purchased the 19 hours SIM which offered free internet for 7 days trial, the SIM didn't work there was no internet access for the entire 7 days

I joined RAIN, purchased the 19 hours SIM which offered free internet for 7 days trial, the SIM didn't work there was no internet access for the entire 7 days. I sent emails to notify the service provider and nothing was done, month end I was sent an invoice saying I owe the ZAR 57 I assume and I queried the outstanding amount and I never got answers. RAIN demanded I pay the amount within knowing not understanding what I'm paying for....