Cannot get Iphone 11 to restore in DFU mode

I have a refurbished 4 month old Iphone 11. Yesterday the screen went black and would not turn back on even with trying the up volume, down volume hold side button trick. It was not dropped and did not get wet. When I got home I plugged it in and the apple logo started flashing every 30 seconds or so but would still not turn on. I downloaded the newest version of Itunes, was able to put my phone into DFU mode and tried to do a restore through Itunes. Before the phone can finish the restore it takes itself out of DFU mode and starts flashing the Apple logo again which creates the error code 4013 on the restore screen. I am going to return the phone to Amazon but am worried that without being able to restore the phone my banking and credit card information will still be able to be seen even without the sim card in it. Does anyone have any suggestions on what I can do to fix or just simply factory restore this phone before I send it back to Amazon? Thank you in advance.