I entered a professional institute which only requires a high school certificate (secondary education). I have a diploma from the same government foundation to which this institute belongs, but they won't accept you if you have any certificate higher than the general high school certificate. So I did not tell them that I have a diploma and I gave them the high school certificate only. They accepted me and I studied with them and learned a profession, but after that I regretted it and repented and I graduated from this institute but I did not take the certificate from them. Is it permissible for me to practice this profession that I have learned with them, or is it haraam for me to practice this profession because I learned it by means of a trick?.
It is not permissible to use tricks in order to study in these institutes and go against the conditions that they have set out, because Allah says (interpretation of the meaning): “O you who believe! Fulfil (your) obligations” [al-Maa’idah 5:1]. And the Prophet (blessings and peace of Allah be upon him) said: “The Muslims are bound by their conditions.” Narrated by Abu Dawood (3594) and classed as saheeh by al-Albaani in Saheeh Abi Dawood.
But there is nothing wrong with you practising the profession that you learned, even if you learned it through a trick or by impermissible means. It is not one of the obligations of repentance that the penitent should forget about the profession that he learned or give up working in that field; rather he should ask Allah for forgiveness for the wrong things he did and work in whatever permissible field he wants.
For more information please see the answer to question no. 69820
And Allah knows best.