Irresponsible Service

I booked a flight for two from Brazil to SEA, USA with CheapO, for this past Aprl (2016).  I'm on the last leg of this trip.  The flight, however, ended up costing us an extra US$1000 due to a "voluntary change of flight."  Truth is, the itinerary I originally accepted with Cheap-O  had an airport change in São Paulo, that would require at least a 5-6 hour window to guarantee connections (including baggage claim, customs and ground transportation).  I chatted with one customer service rep, was promised a call-back by a supervisor (which did NOT happen), talked to at least two other customer service reps, and two supervisors, contacted the individual airline companies and wrote a long letter detailing the issues. (To back up my suspicion, I called an executive cab service in São Paulo...long distance, to inquire as to the viability of the inter-airport transport in the time window given by Cheap-O.  They did the run regularly, and said that the time was insufficient.)  There was NO response from Cheap-O except to say that I, as a customer, had agreed to the terms...and that the penalty for change would come to the above amount.

My question is:  Should a booking company (consolidator or otherwise) not be liable for the itinerary they present as an option?  If an itinerary is not at all viable, should they not take responsibility and make the necessary adjustments without charge to the customer?
I like the Cheap-O website for the most part, but customer service is very poor and, I will avoid using Cheap-O for any service (airline, hotel or car booking) in the future.