hey sergey
its sad to know your encounters, however please wait before you spend any money on unlocking your phone as i have been on this forum and other forums for a while and i am not sure if anyone has unlocked their phone unofficially or paying any amount to anyone.
the mention that apple doesn’t care is not true coz, as you mentioned, there are cases that have been solved and it is ONLY apple that we need to thank coz they are the ones who solved this issue.
the phone that you are using is indeed locked to sprint but if you use the correct protocol which has been mentioned a couple of times, however has been modified by the moderators, is the way that has helped as of now, so you need to send mails to the biggies who in turn send it to apple support who get in touch with you.
Once apple contacts you, you are home from there coz then you are in auto mode, just wait a day or two and they will call you back to simply restore your phone and should be smooth sailing from there.
there is nothing you can do at your end, please use the protocol mentioned and its just a matter of time.
please dont loose heart, apple does care and wont let you down.
you spent a fortune on your phone, just make sure you send the all details of your phone to help them know that you are a genuine case and bought the phone at full price.
the only issue you may face is if the phone was actually bought under contract, coz if that is true and someone sold you a piece that was bought under contract then they may not be able to assist you, coz then the phone may be under contract. You said you bought your phone for 1500 dollars, but to the best of my knowledge the 64 GB iphone doesn’t cost more than 950 USD.
you may wanna check if the phone you bought, was it originally bought at full price or contract? coz on this forum everyone who bought this phone, bought it at the full price.
if you do have a receipt then that should definitely help