You have a full-time job and are also doing a part-time evening course. You now find that you cannot continue the course.
Write a letter to the course tutor. In your letter: describe the situation; explain why you cannot continue at this time; say what action you would like to take.
Dear Sir or Madam.
I am a student of your evening course "Modern English", which is very useful for me because it helps me to expand my knowledge of English. Unfortunately, I am afraid I cannot continue the course.
My problem is that I am going away on a business trip to another city for the next two months. Actually, the trip is unplanned, but, to my regret, I cannot turn it down since nobody can go instead of me. Obviously, I will return after that and I hope to continue your course. I would like to ask you, if possible, transfer the rest of my course fee for the next term as I paid it completely before entering the course because I didn't imagine to brek it. If not, I would like to refund the fee for the rest of term when I cannot study on your evening course. It was not my intention to stop the study, so, I hope, you could accept my situation. As I have mentioned, I am planning to continue you course afterwards.
I look forward to hearing from you soon. Thank you for your cooperation.