Miracles in Islam:
"Miracles(Mu'jisat) take place without any involvement of natural phenomena
by the exclusive act and will of Allah Ta'ala. It is clearly defined in the
Qur'an itself (You did not throw when you threw but Allah did throw - 8:17).
Likewise, there is no involvement of natural phenomena in the happening of Karamah.
They take place exclusively with the act and will of Allah Ta'ala.
This should also be understood that miracles and Karamah do not take place
with the wish or control of the person performing them, but only by the will and act of Allah Ta'ala.
The only difference between the two is that if such an unusual act is
demonstrated through a prophet, it is known as a miracle; and if it is
demonstrated through someone who is not a prophet, it is called
Karamah."
(Ma'ariful Quran by Mufti Muhammad Shafi' vol. 6 page 598)
To clarify further ;
An Example of Mu'jisah -
Musa(as) and the splitting of the sea.
So We revealed to Musa, "Strike the sea with your staff." And it split in two, each part like a towering cliff. And We brought the others right up to it. We rescued Musa and all those who were with him. Then We drowned the rest. There is certainly a Sign in that yet most of them are not believers. Truly your Lord is the Almighty, the Most Merciful. (Qur'an, 26:63-68)
An Example of Karamah - Mary receiving fruits in her chamber.
Every time that he entered (Her) chamber to see her, He found her supplied with sustenance. He said: "O Mary! Whence (comes) this to you?" She said: "From Allah: for Allah Provides sustenance to whom He pleases without measure. (Qur'an, 3:37)
Any acts that seem supernatural done by anyone unholy who is void of Faith are nothing more than illusions, sorcery and the works of satan.
These people who claim to have seen angels, spoken to them or to God for that matter has only experienced the tricks of satan.
Allah(swt) knows best.