FYI - Deliberate and Malicious Deception by Customer Service

What is ATT doing to ensure CS is not receiving credit for meeting quota targets using deception?

You were quite clearly lied to but unfortunately, that is not a question anyone here can answer. My suggestion is to file an FCC or BBB complaint. The complaint will get you a response from corporate, they would have the answer to that question.

I asked to be converted to an international plan for a duration of 3 weeks while I'm abroad.

This one might have been a legitimate mistake or confusion. The only international plan is the International Day Pass, which automatically charges $10 a day for international roaming when used. That option has to be turned on, however; it's not included with any of the packages by default. So the rep was half correct...not the half that mattered, though. 

in order to get me to convert to a new phone plan. Multiple times the agent stated that my bill would be lowered by $12 a month if I switched, when it fact my bill would go up by $3 a month.

Curious... What plans and prices were being suggested?  

It's Not Unusual for the call center reps to have absolutely no idea what they're doing and be wrong. But sometimes they're not wrong they're just lousy at describing it.

Thank you everyone for your constructive input. The same day I wrote this I also reached out to ATT corporate office. I was pleasantly surprised when I was quickly contacted by an executive representative who wanted to understand more about my situation. They confirmed that CS does not have quotas to meet for monetary purposes, therefore the misinformation I was given was in worse case ignorance and negligence. He quickly cleared up the confusion and harm caused by CS. International charges were explained and I was brought back to a phone plan that was the most cost effective. To date the updated plan continues to be the most beneficial for me.

I do appreciate and applaud ATTs efforts to make a long time customer satisfied. This was an example of the customer service I expect from a leading provider like ATT.

I also have learnings from this experience.  Never reach out to CS outside of normal business hours. I will limit CS interactions to my time zone, which hopefully means I'll be in contact with someone within the US.

@rociojs

Or ask on these forums.   Your fellow customers have no skin in the game and therefore no reason not to give you accurate information. It is better to be prepared beforehand than to fly by the seat of your pants and find out you've been given bad info which seems to be the case of your interaction back in August with paid CSRs

As an aside, I can’t speak for that particular rep, but when I worked in the call center we most certainly had quotas we had to reach for monetary purposes. 40% of my “salary” was based on it!