Praise be to Allah.
Giving false information about the salary is lying and is haraam. If wealth was consumed on the basis of that, then it comes under the heading of consuming wealth unlawfully, unless you were in a situation of dire necessity, which would make it permissible for you to lie in order to obtain clothing and the like, because Allah, may He be exalted, says (interpretation of the meaning): “He has explained in detail to you what He has forbidden you, excepting that to which you are compelled” [al-An‘aam 6:119].
If someone is compelled by necessity, it is permissible for him to lie, so that he may receive some of this wealth that is set aside for the poor and needy. However, it is preferable for him to use double entendres.
If you were not compelled by necessity, then it was not permissible for you to take the wealth, even if you were entitled to it, if the foundation stipulated that the salary should not be above a certain limit, and the one whose salary was above that limit had no right to take anything, because the Muslims are bound by their conditions, as was narrated by Abu Dawood (3594); classed as saheeh by al-Albaani in Saheeh Abi Dawood.
With regard to the liability for this wealth, it is subject to further discussion:
- If the foundation gave it to help people whose salary was at the level of your father’s real salary, and you were entitled to receive help, according to the law, as mentioned in the question, then it seems that you are not liable for the wealth, but you must repent from having lied and deceived people.
- If the foundation would not give help to people whose salary was at the level of your father’s real salary, then you are liable and liability is to be borne by those who benefitted from it. Therefore you have to return the money to the foundation by any means, even if it is in the form of donations to the foundation, and the like, without their knowing.
And Allah knows best.