Just checking if you mean individual numbers you have blocked from your iPhone or private/hidden numbers?
Individual numbers which I have blocked. One of these is continually calling, and while the call doesn’t sound and there is no record, it does go to voicemail. This person doesn’t actually leave a message, so my mailbox is full of blank messages, which have to be deleted one by one. I don’t understand why, if the number is blocked, it still gets through to voicemail?
If an individual number has been blocked via the handset, the caller should hear a busy signal.
I just tested it and get the same result as you.
Let me ask around to seek an answer to this, it may take a few days.
I'm yet to successfully find someone who knows the fix for this 😔 I'll keep trying.
I'm told the fix is you need to clear/disable the diversion to voicemail when busy.
Settings -> Phone -> Call Forwarding -> Forward when busy -> Remove voicemail diversion
Something to do with when the busy tone is triggered for the blocked number this then kicks in the diversion to go to voicemail.
This does mean if you're on a call and a non blocked caller attempts to call you, they won't go to Voicemail. Enabling Call Waiting would be the workaround for this.