Why is my iPhone 8 plus having data & Wi-Fi connecting issues?

I just got the iPhone 8 plus today from T-Mobile and I've been having problems with it all day. This is my first time being with T-Mobile and having an iPhone. I also had to change my number. I got home, connected to my Wi-Fi, and tried to get on social media but it was going so slow. Pictures were taking forever to load and videos kept buffering. I thought it was my Wi-Fi so I just disconnected and tried again using my data… Phone was still going slow. SO, I started to trouble shoot. Restarted my phone, turned off data then turned it back on, restarted network settings, updated to the latest IOS, etc etc. NOTHING WORKED! I saw on a website that it's supposed to say "T-Mobile 4G, 3G, or LTE" on the top right corner and it doesn't for me lmao., just says "T-Mobile". The bars go back and forth, sometimes it disconnects and just says "Searching" or "No service." I didn't damage my phone or anything, ITS BRAND NEW! I had simple mobile before and my data worked fine. What should I do? Oh and earlier it wouldn't let me send messages to non-iPhone users but that got fixed i don't know how lmao.

Because when apple releases a new phone they do something to make your phone slower until you buy their most recent version of iPhone

-Samsung is better Apple even uses Samsung parts

. Can more people comment.lmao.i'm looking for an answer that's actually going to help me.

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