Resource Pack Bug

When i play minecraft and change the texture pack, when i open a world, it still doesnt change so what i do is reopen the world and the texture will update. And then when i quit and reopen mcpe again it comes back to other texture pack, not the one im using before. For example when the used texture pack is plastic and then i changed it to city. When i quit and reopen mcpe, the plastic texture is used but i change it before to city. Please fix my phone is galaxy grand prime