How do I pay for my extra test?

Seems like the CB has chosen to take my scores back until I pay for the extra Subject Test I had taken. My scores showed up as normal, were sent to all my colleges and a few have acknowledged that they have received it, but the rest haven’t. Really annoying. So I’ve heard that in the US, you receive a bill in your mail but being international, I’m pretty sure all the communication is done via email. I haven’t been asked to pay yet, and its unfair for them to hold my scores without even giving me a chance to pay up. Has anybody else faced this situation and does anyone know how to pay for the extra test without getting an automatic billing notification?