Hey, thanks for your reply!
I contacted CCBill about it and it seems they blocked transactions from my country.
Here's what they wrote:
Unfortunately, we are currently unable to process decline overrides due to an excessive number of fraud claims coming from your country, resulting in an overhaul of our entire override system. We unfortunately do not have an ETA for when we can expect this system to be back up, and as such you would need to either use a credit card that was issued in the country you are attempting your transaction from, or inquire about alternate billing with the webmaster.
Well, that's a shame.