Sheikh can a person who does major sins and oppression have hope of Allah answering his dua kindly clarify

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The supplication of a sinner may be answered, whether his sin is grave or small, and it is not correct to say that the supplication of the sinner is not answered.

Rather, the Islamic texts mention that the sins may be one of the impediments that prevent the supplications from being answered. However, this does not mean that each sin prevents the supplication from being answered, or that every supplication of the person who committed an act of disobedience is rejected. The supplicator who insists on disobedience may have done some righteous deeds, or that he invoked and supplicated Allah with sincerity and humbleness, and so forth, that may be a reason for his supplication being answered. Rather, Allah may answer the supplication of a disbeliever (non-Muslim).

Shaykh al-Islam Ibn Taymiyyah said in Majmoo’ al-Fataawa (1/206):

“All the creatures ask Allah both the believers and the disbelievers, and Allah may answer the supplication of a disbeliever. The disbelievers ask Allah for livelihood and He provides them with sustenance and drink, and when adversity touches them at sea, lost are [all] those they invoke except for Him. But when He delivers them to the land, they turn away [from Him]. And ever is man ungrateful.” [End of quote]

Al-Bayhaqi narrated in Shu’ab al-Eemaan (2/385) from Ibn Uyaynah who said: “Do not abandon the supplication, and what you know about yourselves [i.e. your sins] should not prevent you from supplication as Allah responded the supplication of the devil while the devil is the worst of all creation.” Allah Says about the devil (what means): {[Satan] said, "Reprieve me until the Day they are resurrected."} [Quran 7:14] Allah responded to him Saying (what means): {[Allah] said, "Indeed, you are of those reprieved."} [Quran 7:15]

For more benefit on why supplications are not answered sometimes, please refer to Fatwa 418060.

Allah knows best.