T-Mobile is holding me hostage!!!

I financed an iPhone 11 back in 2015, after paying it OFF they should have unlocked my phone. Well they didn’t, eventually I closed my T-Mobile account and used lycamobile because it’s the same thing but half price, THEN a year ago I switched to mint mobile, same price, more benefits. Now im trying to switch to Visible because same price MORE benefits including unlimited hotspot which is perfect for me as a nomad but I can’t because my phone is carrier locked with T-Mobile/Sprint. After MANY calls to customer care and a trip to a store in person they were not able to unlock my phone due to me not having a RECEIPT that shows I bought my phone OVER A DECADE AGO….. like be so for real… they are able to pull up my old cancelled account but only partially?? So they can’t exactly verify if my phone was bought through T-Mobile BUT they are able to verify all FCC guideline's to unlock my phone through my imei number yet they still refused. The person in store said i might as well get a new phone because my iPhone 11 will stop system updates because it’s old even though it works perfectly fine! Like I had to file complaints with the FCC and BBB and call multiple times!!! They DO NOT want you to have autonomy over what carrier you use!!! It’s a nightmare!!! I don’t want to pay over $500 for a new phone just so I can switch! This is ridiculous! It makes no sense why they won’t unlock my phone. It feels like such a scam, then when I told the sales guy at the store i pay $40/mo with Mint Mobile he said it was expensive and proceeds to show me their options that were the exact same price or MORE EXPENSIVE but gave LESS benefits?!? Like woah next time just slap me silly!!!! It would hurt less!!! Im thinking of switching to a flip phone and just use my iPad on the side! Late stage capitalism is really doing a doozy on us all!!