1- It’s possible that the person was really in need, but it’s also possible that he was making up those stories to get more money.
2- In any case, you helped him and you fulfilled your duty. Now what you can do is give some charity to a trusted source (like an orphanage or a charity you trust) and ask Allah to remove any negativity from your life. It’s best to have a sheep sacrificed and given to the poor.
3- Write Ayatul Kursi (2:255-257) while on Wudhu and towards the Qiblah and post it in every room on the wall.