Why isn't my mobile hotspot working?

I got a new phone on Black Friday because it was on sale. It's a iPhone 6s. My previous iPhone's mobile hotspot worked perfectly fine. My phone plan is T-mobile. It hasn't been letting me use it ever since I got it. I tried it at my dads house to see if maybe the connection was bad where my mom lives ( There's great connection at my dads house ) It did the same thing. It's not because I don't have data because I'm on T-mobile, plus I tried it today and it's the day after I just payed my bill so my data should be at its maximum.
When I click the "on" button it does pop up on my Laptop's Networks. I click "connect" on my Laptop and it says it is taking "Longer than usual to connect" and then finally it says "Can't connect to this Network"
I know it isn't the Laptop that's wrong because it connects to my moms mobile hotspot, my cousins ( she has the same exact phone) and it worked on my old phone. Please no useless answers.

Data doesn't reset when you pay the bill. It resets when the cycle is over.

Contact T-mobile and ask to be connected to TECH SUPPORT and have then walk you through a few trouble shooting tasks. It is either you plan is no longer provisioned for Hotspot access on your account, or the phone is defective.

Make sure you call from a DIFFERENT phone that is NOT the phone with the issues, because if any steps involve rebooting the phone, you will be disconnected from the tech helping you, you will then have to call back and start all over with a different person.