More than likely you didn't pee on the stick enough, but read the directions and follow them perfectly those little test sticks are sensitive and won't work properly if not used properly, you can call them and complain they might send you some coupons for future products or they just might tell you the same thing
Most of the direction say to urinate on the stick for 5-7 seconds I always pee for 10
seconds to be sure or most tests have direction for peeing in a cup and dipping the test stick in there.