What is the way to get rid of obsessive-compulsive disorder (OCD) that leads to hearing ugly speech and having intrusive thoughts that cause fear of shirk (polytheism), despite adherence to acts of worship and seeking refuge (through supplications)?

Waswas (whispers/obsessive thoughts) do not cause harm as long as they are disliked and shunned. Your aversion to them is a sign of sound faith. One should not give these waswas any attention, as they are from Satan to deter you from righteousness. The servant is rewarded for struggling against waswas and ridding themselves of them. It is recommended to adhere to the supplication: "O Allah, I seek refuge in You from associating anything with You knowingly, and I seek Your forgiveness for what I do not know." Also, strive to learn Tawhid (Oneness of God), as it is the greatest protection against error and deviation.