I had used a Matrix sim card for Hongkong with bill no HK3476004 and being a post paid system it was super convenient for me. While I had used their sim cards for various other locations as well in the past, I never faced any issues with billing at all. And this time as well I landed up paying some few thousand rupees as my usage charges but all were justified. Every call rightly recorded and reflected in the bill along with the charges. I really like their way of making things transparent and clear. Good work !