IPhone 4s blocking

[Fupfamilysurvivor]

NC with father but somehow he's managed to leave a voicemail even though I've blocked both his numbers. How? And how to fix?

Blocking the number on you phone simply means that your phone won't accept calls from that number. It doesn't stop the caller from leaving voicemail. That is controlled by your mobile network, not the phone. And if your father calls from a different number or blocks his caller ID by dialling 141 before calling your phone has no way of knowing that the call is from him.