If your wick has a giant ball forming on it then it is a carbon build up and is commonly referred to as "mushrooming".
Don't fret, your candle is not defective and is still perfectly safe to burn.
So what causes "Mushrooming" of the wick?
The scent and dye used in making candles can sometimes collect in the wick which essentially creates the "mushrooming" carbon ball. Soy candles are usually clean burning, but when you add scent and/or dye to the wax it affects the burning properties. This is easily fixed by simply trimming the wick to 1/4 inch after each successful burn of your candle.