But that happened before the advent of Islam.There were hardly any Christians in Mecca or Medina, if Quran is correct about the Christians, there is no doubt about that; then the Quran must be correct about the Jews of Medina.
This is an absurd argument. The Qur'an got one thing right, and therefore all else must also be right? I can say that Jews worship God. That's true. Therefore, when I go on to say that Christians all worship a cat with butterfly wings, I must be right again.
This obviously doesn't make any sense. One has to test claims individually.
THE MYSTERY & HISTORY OF THE JEWISH PEOPLE: AN AFRICAN PERSPECTIVE
By SAM OYSTEIN
Please note from the above that there existed some groups of the Jews who later became extinct.
Right, Jews are variable. It would be bizarre, but technically within the realms of possibility, for there to have been a denomination of Jews in Medina who thought that Ezra was Son of God. The Qur'an, being a perfect book, would surely have put 'the Jews of Medina' or something along those lines for basic clarity. Rather than saying something analogous to 'Humans are from Egypt' when in fact only one small sub-set of humans are from Egypt.
But I will reluctantly concede it on the grounds of the unprovable and undisprovable nature of your claim here. Or rather, that of the Qur'an.
One I would really like to address is 25:53:
"And He it is Who has made two seas to flow freely, the one sweet that subdues thirst by its sweetness, and the other salt that burns by its saltness; and between the two He has made a barrier and inviolable obstruction."
There is no inviolable obstruction between seas. There is a barrier which allows for diffusion.