Roaming data bill R122000 in free wi-fi area

We travelled to Brazil & Peru from 13-30 Dec 2015. The 1st night we slept in Sao Paulo Marriot Hotel where we had free w-fi in the hotel & shuttle bus. I used the free wi-fi until we left on 14 Dec for a cruise along the coast of Brazil. We were on the cruise for 5 days until 19 Dec. We were on the open seas with no cell phone coverage. We docked at a few villages where I also didn't have network coverage. The 18th Dec we docked at Ilha Grande. There I got coverage and sent a few whatsapps Then we went to Rio de Jainero from 19-24 Dec & stayed in Porto Bay International Hotel with free wi-fi. After that we went to the Amazon 24-29/12. In the jungle there was no network coverage. 97% of the time abroad my cellular data & data roaming was switched off. I got a sms from Vodacom on 23/12 (I was in free wi-fi zone) to say my usage is R117316.41 & again on 28/12 (while I was in the Amazon with no internet connection) to say it is now R121684.69. I only made 2 phone calls (30sec & 2min), sent 1 e-mail & couple of whatsapps. Most of this in free wi-fi zones. I reported the matter when I got back. Vodacom offered me a discount but I must still pay an astronomical amount. I dispute this.