Disclaimer: It has been close to 10 years since I had to call for support from an América Móvil company (StraightTalk, Tracfone, Net10, etc.) So this information may be outdated OR I might have 'mis-remembered' some of the details.
América Móvil call centers were in Miami and Mexico. Early morning calls tend to be directed to the Miami center while calls later in the day and at busier times will more often go to another center.
The Howard Forum had a thread running at one time that listed a phone number that went directly to the Miami center always. It also listed a few email contacts of 2nd tier support that could solve problems and skip the 1st level. I was able to use this method to solve several lost minutes, expired minutes and account expiration problems.