No service for my "unlimited" plan! Can't make calls or texts without being connected to wifi?

Since I got on a new plan with t-mobile in 2022, I've been having issues receiving and sending texts and calls. I'll need to be connected to wifi most of the time to have service but I'm paying for an unlimited data plan and rarely have service when I'm out. Tmobile is stealing from me, I should not be paying this much to constantly be out of service! Especially when I need it most while I'm commuting or traveling. I recently got an unlocked phone compatible with tmobile from backmarket, not expecting much but once I put my SIM in the phone, this problem got 10x worse. I troubleshooted the network with customer service but nothing changed, and got a new SIM and the service did not improve. But now I look at my account online and it says the model of my phone is an iphone 12 when I actually have a samsung galaxy FE???? I'm so confused and I want my money back!