Issues receiving calls

Hello,

I am getting issues with my (fairly) new iPhone 11 Pro Max. The firmware is up to date.

The issue has only been happening for the past few weeks. The fault is that when I receive a call it doesn't ring at my end. The person calling me gets directed straight to my message bank. It eventually shows up as a missed call. If they call back again (in a fairly short time) I get the call as normal. If they call back at a much later time (I am not sure of the timing) the fault occurs all over again.

This problem is REALLY frustrating as I use my phone for my business and I am missing MANY important calls. If the caller doesn't phone back I can potentially miss business opportunities.

Can someone advise if this is a fault with my iPhone or a Network issue (I am with Telstra for mobile service). I can't be certain, but the problems might have started around the same time as I saw techs working on the local cell towers and installing new 5G services in my area. I am not sure if this is a coincidence or the cause of my issues.

I just purchased my co-worker an iPhone 12 Pro Max and his very new (only a day old) phone doesn't appear to have the issue. He is also with Telstra.

Has anyone experienced the same issues recently. I had been told by others that there had been Network issues but I cannot substantiate these claims at the moment.

I would really appreciate any help.

Thanks.