I learned swimming quite a long time ago so I may be wrong, but I think the point of kicking is mostly to keep balance. If you have good balance, you are able to swim freestyle even without kicking (legs just floating and rolling with your body). If the legs won't stay up, it's a balance problem, not a kicking problem most of the time. There is no need to really propel you forward with your legs (at least if you aren't a competitive swimmer)... so don't be discouraged.