Trying to mount a 50' TV on a wall. No studs behind drywall. Drywall is about 4 inches thick. I have not found anchors long enough. HELP!!?

Update: I have drilled a hole with a 1/2 inch drill bit and it seems to be drywall all the way through. I never imagined the wall would be so thick hence why I didn't simply drill a small test hole. I have tried snaptoggle anchors but they cannot reach all the way through to hook on to the backside of the drywall.... show more I have drilled a hole with a 1/2 inch drill bit and it seems to be drywall all the way through. I never imagined the wall would be so thick hence why I didn't simply drill a small test hole. I have tried snaptoggle anchors but they cannot reach all the way through to hook on to the backside of the drywall.

The wall area is located above a fireplace if that means anything. Also this is in an apartment so can't exactly do too much with the wall.
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