Voice-Mail Delay On iPhone 12 Pro

I received two "Missed Calls" from my Doctor's office but no voice-mail.

One was on Tuesday, the second on Thursday.

It was very urgent and important that I get test results, but there were no messages.

The following Monday, seven days after the first call, 2 voice-mails show up on my phone.

They were connected to each call, but didn't show up until several days later.

Before you suggest every typical solution, Yes I update the phone software,

and I restart the phone every few days, and checked the settings. It should be in perfect working order.