Issues with conference calls

Hi all. I am having an issue with conference calls on my iPhone XS. I use Verizon.

1. I am unable to add more than two callers. The add call feature is grayed out.
2. When I am on a conference call, instead of listing who is on the call, as it should, it says "Multiple Callers"
3. I am hit or miss on being able to merge calls. Sometimes it works, often it doesn't, and I am dropped from the call regularly.

Here is what I have tried:

1. Turning off wi-fi calling
2. Turning off VoLTE
3. Resetting my network settings

Would love any and all thoughts or feedback, as I am not able to get an appointment to speak with someone at Apple until May 6th, and my job requires my ability to utilize conference calls (and zoom/webex are not always options).

Thank you!