Sorry for the trouble - it is always complicated when connecting from a domestic(-ish) airline to an international one. GOL employees at outstations might be contracted, and they probably rarely deal with international connections.

thoughts: maybe you could have asked GOL to check in to GRU only - flight being domestic they won't bog you too much. At GRU there would be real AAgents who would know the rules. But in this case, I would call AA again and explain the situation succinctly (unable to check in due to bad GOL agents, had recordings/calls to AA CS during check-in they could listen to etc). I think eventually someone at AA would be happy to get it rebooked