BEWARE OF ********** BILLING BY VODACOM

I was recently on a trip to Italy, Nepal and India. I used only wifi, I do not have voice mail set up and I do not answer calls. I answered one call on the day of the earthquake done by my son. The phone call was less than one minute. My charge for the month is R6200. I requested itemised billing only to find that all wi-fi activity was charged as roaming. I used two sim cards which I swapped - one was on contract and one pre-paid. I used them with the same settings. The pre-paid sim had no credit on it which means that I was only using wi-fi. Why then am I being charged exorbitant amount on my contract sim for the same activities? My only answers is that VODACOM has charged me **********ly as a customers.