Find my iphone Scam

I bought a Amazon certified phone and send it to T-mobile warehouse Texas for trade in program and I got an email saying they got the phone however they didn’t give me any credit. When I asked they said find my iphone is still turned on that is why I didn’t get credit, which is 100% not true. Amazon never sell phone without resetting and I also checked everything before I sent the device. Amazon also sent me the proof that find my iphone is turned off on that device, and they said there is also a website to check with device imei number to see if find my is turn on or off. They did Handset… research form, but when I read the problems of other people now I have no hope. Any suggestions?