I am trying to move from Tmobile to ATT. I have a Samsung S20+5g and its saying to get it unlocked by sprint

I am a bestbuy employee and had an accomodation when they worked with sprint. I bought my S20+5g outright and Tmobile took my accomodation away 3 months ago and im trying to keep my phone and move to ATT . The phone keeps telling me that its locked to sprint and call them. Well, Tmobile is sprint now. They tell me its unlocked from Tmobile. CS tells me to go to connections>more connections and unlock sim….But on my phone there is not unlock sim. So I spent hours with these “reps” that dont know a thing. Then they connect me to Samsung and Samsung says that I need to go to a Tmobile store, the guy at the store is like “IDK” , he says call CS. This is BS. Oh, and Samsung said they will give me an accomodation and upgrade me….yeah for $600 more.  I heard that if you report them to the FCC, they will fold and help you. Anyone else with this problem??