You saw an advertisement for a tennis course in England but you have one or two problems

Dear Sir or Madam

I am writing this letter to your company in order to enquire the details of the tennis course in England,which posing (do you mean to say which was posted?) on your company's homepage.

I have been playing tennis for years. In fact, I am a tennis enthusiast who is always seeking a formal tennis course to improve my skills (abilities is a better word).However, because of some personal reasons,it is difficult to have such an opportunity for me.Since my co-operation is going to send me to England for business, so that I can enroll in the tennis course.Before joining I would like to know whether I have to bring my tennis tackles with me?Also if there is a lunch included in the course?

The second thing is my concern about the length of my visit because I will only be staying in England for no more than a week.Thus, I might be unable to finish the all of the sessions.So I want to know is it possible to get a partial refund if I could not complete the course and leave earlier?

I am looking for hearing you.

yours faithfully

Angus

(Explanations)
Dear Sir or Madam

I am writing to enquire about the details of the tennis course in England (here you should add the name and dates of the tennis course. This company may have multiple courses in England.), I saw a posting about this course on your company's homepage.

I have been playing tennis for years. I am a tennis enthusiast and am always seeking formal tennis courses to improve my skills. However, because of personal reasons, it has been difficult to find opportunities to attend courses. (If you are sending an email to someone you don’t know, they don’t care about your personal situation. You can just delete this) My co-operation is going to send me to England for business, so I would like to enroll in the tennis course. Before registering, I have a couple of questions. Do I need to bring tennis tackles? Is lunch include with the course?

I will stay in England for no more than one week. Thus, I might be unable to finish the whole session. Would it be possible to get a partial refund if I must leave before the completion of the course?

I look forward to hearing from you.

Yours faithfully,

Angus

Your letter is very good.  I changed some of the language, not because it is wrong, but because it does not sound natural in this particular setting.

You saw an advertisement for a tennis course in England but you have one or two problems

Dear Sir or Madam,

I am writing this letter to your company in order to enquire details about the tennis course in England, mentioned in the advertisement posted on your company's homepage.

I have been playing tennis for years. In fact, I am a tennis enthusiast who is always seeking a formal tennis course to improve my skills. However, because of personal reasons, it is difficult to find such an opportunity.

Since my company is sending me to England for business,  I wil be able to enroll in the tennis course. Before joining, I would like to know whether I have to bring my own tennis rackets or if they are provided? Also, is lunch included with the course?

The second thing I have a concern with is that I am only staying in England for one week. Therefore, I may not be able to finish the entire course; would it be possible to receive a refund for the sessions I don't manage to attend? 

I look forward to hearing from you.

Yours sincerely, 

Angus