Phone doesn't ring when someone calls me, outgoing calls don't connect 3-4 times until they do

I have a Samsung Galaxy S8+. I've been using a prepaid multiline account for about a year now and all was fine until a few weeks ago.

When other people call me, they go to voicemail almost immediately 90% of the time. When I call other people, I don't hear anything at all, including that initial beep that lets you know you're connected. I have to retry a couple of times to get it to call someone.

I know it's not an issue with the region's signal since my friend in the other room is connected and fine. I also have no issues with data or text messages. I get 4G data all the time. I'm not in 'Emergency calls only' mode.

I have tried a power cycle, taking the SIM card out and cleaning it.

Do not disturb mode is OFF.

Airplane mode is OFF.

Calls aren't blocked.

When I go to check call forwarding at Supplementary services per the troubleshooter, It says:

Failed to read data

Something went wrong, Check your SIM card or network connection and try again.

I have to explain to everyone why I'm not returning their calls.