slavs arrived only around 550 in that area that is today FYROM is a fact and can also be read on old church documents.
Indeed, they arrived in the area called Macedonia and remained there ever since. Does that mean the name of the area has been changed since then?
So you're recognizing the existence of the country of Macedonia? Good for you!
Greece should stop insisting on the nonsense concerning the name Macedonia as soon as possible. The folk who lives there is different than in the times of Alexander the Great, but the area has retained its name in continuo
. Nothing special about it really. The territory of East Prussia, for example, was once inhabited by some Prussian tribe (Baltic folk), but in the mediaeval ages the Prussian language disappeared after the Teutons of Germanic origin came there invited be the Masovian prince Konrad and later on conquered the whole land. Then settlers from Mazovia also came in and settled in southern parts of East Prussia. Nevertheless, the land had been retaining its original name 'Prussia' all that time and the name was even passed onto the whole Kingdom of Prussia until 1945 when it crashed under the strength of the invincible Red Army of the Soviet Union.
Second, the Greek language in its classical form sounds of course completely different to modern Greek. No way that Alexander the Great could ever comprehend modern Greek! I remember that I once read in the memoirs of a British aristocrat being fluent in classical Greek how he went to Greece in the 19th century and started talking to them in that ancient language. In reply, the 19th century Greeks stared at him in bewilderment and simply said nothing to that weirdo. And this is yet another reason why Greece should say good-bye to the ancient Greek Macedonia and stop being silly in opposing the modern Slavic Macedonians choosing the right name for the country they inhabit.