What is the ruling on studying and the stipend paid if a student was admitted to the bachelor's program by using a friend who took the English language exam on his behalf, and must he leave his current studies and enroll in an expensive evening program to clear himself of sin?

What you did is forbidden forgery and deception. You must repent of it by seeking forgiveness, feeling remorse, and resolving not to return to it, and by not using the certificate for which your friend took the exam on your behalf. As for continuing your studies and benefiting from their advantages, it appears there is no harm in it, due to your consistent attendance in the course and your study of the material, along with your fear that you might not achieve the required grade. If you were to leave your studies now, it would result in harm. You can strive in your studies and develop yourself to strengthen your abilities in the required linguistic material. Sheikh Ibn Uthaymeen issued a fatwa permitting entry into university for those who cheated in previous subjects, after repentance, provided they avoid cheating in the future.