First of all determine the root cause of why you can’t lose weight, doing more cardio isn’t going to solve the root cause, insulin resistance, you control the hormone that is designed to store fat you will lose weight. It is all about balancing your hormones. When you understand how the BMI works it will all make sense.
You need to be in a caloric deficit consistently to lose weight. You can achieve this by consuming LESS calories via food and drink and by expending MORE calories via physical activity – a treadmill can help with this but be wary that the majority of weight loss will be dependent on you consuming less calories.