Iron is a non-combustible material but when it is bought near flame it produces heat then shouldn't it be combustible because it produces heat as rusting of iron is a slow combustion because it produces heat?

Combustion of the metal produces smoke, heat and light normally. ​Iron has a very high ignition temperature around 1450 ⁰C, only at that temperature combustion of iron takes place. This temperature is the noncombustible temperature given by the ASTM standard. That is why iron is considered as a non-combustible one.
No relation between combustion and rusting. Rusting is a different property in which iron get corroded and form its oxide Fe₂O₃.xH₂O.