I think the main problem was the luggage, they could not check it in to the final destination. If you have travelled with hand luggage only, there wouldn't be a problem in my opinion.

Also wondering if you re-packed the stuff, throw away the big suitcases and go boarding. That might work.

The staff could be also not helpful if they've checked the price of your ticket from VCE to GRU, which was around 150€ rt I guess (on the famous error fare). This is S.America and still customer service is not that helpful and "above and beyond" as we usually have in Europe.

Very strange they cancelled your ticket from GRU. Or they rebooked it for departure next day? If not, then this was very mean.