Calls go straight to voicemail - phone doesn't ring (Samsung S6 on Nougat)

This might not work for everyone, but what worked for me was turning off Wi-Fi Calling (Settings > Network & Internet > SIMs > T-Mobile > Wi-Fi calling off). I have a Google Pixel 6a running Android 13, and people were complaining that they had to call me 2 or 3 times before my phone would actually ring. The first 2 calls would go straight to voicemail, and I did not receive a missed call notification on my phone. Somehow I think that the phone just misses the call as it’s trying to decide whether to route the call over WiFi or the T-Mobile network.

I'm in the same boat. My issues started in June after Visual Voicemail update. I have a Google Pixel 6 Pro (unlocked) that is just a little over 1 year old and running Android 13. I ended up getting rid of VVM and just using Phone app. 

I got a Pixel Watch (LTE) n July and things got worse. In desperation, I started using Google Voice. Still had issues. 

By first week of August l, I uninstalled Google Voice, not using VVM, did reset codes, and set up regular VM. I don't have DND, no bed time schedule, did codes to reset any CF, soft reset of phone, and checked all settings.

Talked to customer service then tech support numerous times. They checked multiple issues and said everything is fine including number of rings. I would get transferred and then call would disconnect. Guess what when they call back goes straight to VM! They suspended my new smart watch line temporarily.

I drove to store per instructions to have them check existing Sim in store in another phone. They gave me new Sim, but would not call customer service from there. I had to call myself and was told to do hard reset. It didn't work! Plus ticket to Engineering has never been resolved.

BTW, I am trying to sell home & car plus have a bunch of medical issues. I can't deal with constantly missing calls. I know Verizon is expensive, but I am fed up with this.