May I suggest changing your wifi password? Someone may very well be leaching off your wifi. I suggest a password change and also change the name of your network to something like (insert city name) Drug Enforcement Agency. It works very well.1024 is what my cap is also, it's 1 terabyte.
I have lost 3 people out of my house 2 moved out after being told they needed to and our older son went to college...it's August 13th and I sit at 1500 GB's used. Apparently gaming is the destroyer of bandwidth.