Has any adult-onset swimmer succeeded in increasing ankle flexibility?

My ankle inflexibility seems to be a huge drag to my freestyle and backstroke. In my attempts to increase ankle flexibility, I have employed a couple of methods suggested elsewhere in this forum - (1) assuming the "child's tv-watching" position, with my lower legs folded beneath my buttocks and (2) using fins. However, after three months, I don't seem to have gained any more flexibility in the ankle joints. Have other adult-onset swimmers been able to gain ankle flexibility through these methods or otherwise?