Situation: I am the 1st Player. In area with my block (A) Im moving my another block (B). My turn ends. Then enemy moves his block in that area and claim my block B as reinforcement. What could you say to my opponent?)
Your opponent is wrong. You are not the attacker, so the blocks you moved in are not Reserves (5.32), and you're not Player 2, so your blocks are not Reinforcements (5.33). Both of your blocks can fight or retreat in round 1.
(Those references are to the version 3.0 rules.)