IOS memory can't release

There are two scenes in our game. Scene A is an empty one while scene B has some resources within.
When we verified memory usage under the xcode we got the following issues:
1、The memory usage was 35M when we entered scene A first time.
2、After we entered scene B it increased to 50M.
3、The situation is the occupancy reduce to 45M when we went back to scene A.
It should be 35M if we free the memory of scene B completely.
Then we switched these two scenes frequently, the memory usage didn't get bigger.
There is also the problem of memory enlargement when we use Resources.Load() or instantiate objects.
And Resource.UnloadUnusedAssets() can not release these memory whitout references properly.

please help