Service drops

I have an iPhone 18 pro max. Just got it almost 2 weeks ago. I’m having an issue where the phone drops my calls daily. Once in the morning usually around 11 am -11:30 am and then again 2 am -2:59 am. It really only lasts 15-20 seconds and the service is back right after. I’ve called T-Mobile and they advised their engineering team said it was WiFi calling, I turned that off and I’ve left it off since they advised to keep it off and it is still occurring. Not sure what to do? Is anyone else experiencing this on an iPhone 18 pro max or any phone?