while I'm glad I can say that I've not had the same problems I wish I could help but I have not had any missed calls or texts on my 6T.
Are you using the default Samsung Messages app for texts and the stock Samsung or T-Mobile dialer for calls?
Ah shucks, it's super important to get those calls. Are people getting routed to voicemail? We do have some common steps on can follow on our Can't call, dropped calls, & other calling issues page that can help.
I'm hoping that since we haven't heard from you in a few days that you were able to get to the bottom of why you're S9 can't receive calls. If for some reason you're still having issues, please take a look at the questions from the previous replies and get back to us.