Fortunately or unfortunately, telcos do not follow the same "logic" that credit card companies have. For credit card companies, once you exceed your limit, the following charges would be declined. However, for Globe, they assign you a credit limit (in my case I had used to have the plan 599 with a credit limit on my billing statement showing as 2,500) but they don't automatically hinder you from using your phone line even if you have exceeded it. I don't exactly know why but I think it's because their system is not "trained" to hinder calls/texts/internet consumption past the assigned credit limit. I had to learn this the hard way when I had a similar experience. Thankfully, mine was disputed. Although I would have to say that I was really pissed that time cause the credit limit seemed to be a useless thing to have. When I applied for a second line and when I re-contracted that's when I learned that the credit limit does play a part.
As for roaming, it really comes with a price. Calling from Thailand to the Philippines was 110 pesos per minute and it was a headache when my bill ballooned to an amount that was far from what I'm used to.