Sometimes, despite your best efforts, a starter just will not react as you had hoped. This can come down to a variety of factors including quality and age of flours, water quality, as well as temperature and environment. If you haven't seen any doubling within 10 days of starting the process then I recommend you start from scratch again. Before 10 days, you can try to place the starter in a warmer environment such as an oven that has just been turned off or try feeding the starter a different type or brand of flour.