A blocked SIP Trunk, that is of course not something you want. There are a few possible reasons why your account has been blocked.
Not enough prepaid balance: In order to send voice calls with a prepaid account, you need to have at least a balance of €5,- available. If your account drops below this threshold, the account and related SIP Trunks will be blocked. You can get your account unblocked, by topping up your account and contacting firstname.lastname@example.org to unblock your account.
Fraudulous or spam traffic: Sometimes your SIP trunk is being used for fraudulous or spam traffic. If we suspect fraud traffic, we may block your account. Support will brief you via e-mail or phone if this is the case.
Billing disputes: In the unlikely event of a billing dispute, your (voice) accounts and related services might be blocked until billing disputes have been settled.