About the achievements

I don't know about other players but my  problem is serious . When I was playing minecraft I decided to do a survival world cuz I only had creative ones so when I was playing it I found diamond ore and when I mined it with my iron pickaxe it gave diamond , I was very happy at that time but I realised that my achievement 'DIAMONDS' has not been unlocked I tried to restart game but it didn't show any result I was very angry and I started writing this . I have a proof , the screen shot underneath If you think I have used cheats or in creative you can check It I will give the permission If you want