Currently in Mexico. Out of curiosity, I tried to reload online through MiTelcel again. This time I went through a process where I had to put in the amount in pesos they charge (under $1) as some sort of verification step. You're only given two attempts before the reload is cancelled altogether.

Of course, even after being able to complete verification on one of my cards (which required some calculation due to US banks only showing USD amounts), it still failed to reload. Not to mention that I ended up getting a fraud alert and needing to call Chase for my other card.

Oh well.