You don't have the One M8. Those photos look like its predecessor, the M7. The M7 does not have SD card slots, with the small exception of Chinese versions of the phone. Basically the radios for Chinese bands can be smaller, making room for an SD slot that is accessible with a removable back plate on the M7. If someone sold this advertised as an M8, you could try to get a refund through a false advertising claim. Given the age of that phone (came out in 2013), it isn't going to be worth investing a lot of time into chasing down a refund.