Camera won't turn off!

If when you switch the camera off the camera doesn't react in anyway, there's a decent chance the power switch may be broken. To see what's going wrong with it, you'd need to remove the top cover to be able to see the switch from underneath the cover. Unfortunately, there isn't currently a guide on how to remove the top cover on the Rebel T7. There are guides for the Rebel T6i and Rebel T5 (follow up until Step 12) which would still help with the disassembly and most steps will probably be very similar to your model. The Rebel T6i is only a generation down from the T7, however sometimes Rebel T models that are multiple generations apart will sometimes have more in common than a Rebel T with with a Rebel Ti even in the same generation (when it comes to the camera construction anyways). Since there may be some minor differences, just keep a really close track on what screw goes where.

Once you have the top cover removed, you can take a look at the bottom of the power switch (marked in the image below). If you flip the switch on and off, you'll see the metal piece sliding up and down. A signal is passed through the metal piece from the pad on the top, to one of the two pads on the bottom. Which pad on the bottom it makes contact with (and passes the signal through to) tells the camera which position the switch is in. You'll want to check to see if there is any dirt or debris that could be preventing the metal pins from making contact with those pads. Also visually inspect the pins to make sure they aren't bent or damaged.

If the pins are bent, you could try to use a pair of tweezers to carefully bend them back into position. If the pads need to be cleaned, you can unscrew the metal piece to get it out of your way. Then use a cotton swab and some isopropyl alcohol (>90% concentration) to carefully clean off the pads.

If the pins are beyond repair or you're unable to fix the issue with the switch, replacing it would be the next option. Unfortunately the top cover is considered to be "unserviceable", meaning that it's probably unlikely that you'll find a replacement switch. If not, you'll have to replace the whole top cover (just search "Canon Rebel T7 top cover" on eBay).