What rights do we have after being 'abandoned' in Guatemala during a technical stop?

We flew Barcelona-Managua return with Iberia this July/August. At Barcelona we were given boarding passes for changes of plane in Madrid and San Salvador.

When we arrived in Guatamala we were told that everyone had to get off the plane with all their belongings and to go through a security check. We double-checked with the cabin crew as we had no scheduled stop there, but were told that we had to all the same. We left the plane and followed the directions of ground staff, showing our boarding passes and asking too (my wife is Spanish, so there were no language issues). We were directed to a waiting area with various shops, cafes and gates.

Despite continuous attempts to get information, we were made to wait until an official told us that our plane had left hours earlier. He told us to leave the secure area and marched us to/through immigration.

Getting on another flight with our ticket also proved difficult to impossible, as we were told we would have to wait a minimum of 48 hours for an available seat, and even that had no guarantee.

Eventually we bought tickets using our own money and flew to Managua, arrived a day late, missed a meeting, without luggage (which took another 3 days to sort out), and with hotel penalties, etc.

Speaking to the staff at the airports and other travellers, we learned that this is not the first problem of this type with Iberia in the area.

What rights do we have and, above all, how can we get the money back for the flights we were forced to purchase?