I do not have any balance on my account anymore. But why may I not still use it?

JonDonym-accounts may only be used temporarily and just with a single rate. If you do not have any balance anymore the account is not usable anymore, too. This prevents that JonDos or a third party may recognize your accounts on the long run and may thus be able to count your spent data volume.

Why does my account loose data volume?

The settlement of JonDonym-accounts is volume-based. If you are surfing you are sending and receiving always a data volume. And you are paying the provider of JonDonym-services using your data volume on your account automatically.

Why do I already loose some MByte of my data volume on my account, if I am just connecting to premium-services without surfing the Web?

The payment by volume is always done in advance. Otherwise, clever hackers could use JonDonym-services free of charge while surfing the Web. That is why JonDo creates a mini-account up to 3 MByte on every premium-service you have once been connected to. Every time you are connecting to the same service again, the balance on this particular mini-account will be replenished to 3 MByte.