I have been prescribed methylcobalmin 1000mcg/ml injection but i am able to get either cyanocobalamin or mecocobalamin.could i use either of the two?

Yes, probably : Cyanocobalamin is an artificial B12 which must be activated in the liver. Methylcobalamin or Mecobalamin is a biologically active form. Your doctor may have a reason for preferring the active form. BTW, Mecobalamin is fully absorbed through the mucous membranes of the mouth, but cyanocobalamin is not and must be absorbed through the gut (unless injected).