SD card won't lock in, card cannot be accessed when door is closed

The SD card to my second-hand EOS Rebel T2i does not lock into the slot. When I shut the door to the SD slot the camera displays “Card cannot be accessed, Reinsert / change card or format card with camera”. I have formatted my SD card with both my camera and a program on my computer to no avail, I have also tried changing the SD card which also changed nothing. I have attempted to look in my town for a camera repair place, but I don’t want to give it to cannon because they are way too overpriced, as i bought a battery marketed as $50 for ~$7.