I wrote a adjustment letter to practice in English. Please tell me if there are any grammatical errors.
Dear Mr. Yamada:
I was very sorry to read your letter telling me that we failed to supply computers that you ordered. We will do my best not to repeat such a thing ever again.
To resolve that, I have already got in touch with the president in your company. Your president asked to replace them with new computers to your office with no costs. Therefore, we will provide the new computers as soon as possible.
We realize that your employees have an inconvenience situation during the working hours because of our computer failures. To make up for our underperformance, let us give you a 15 percent discount coupon for your next orders.
You have been a good customer since we started an office supply business. We would not like to spoil with our relationship with you because of our computer defects that we had this time.
Please contact me at Yamada@gmail.com or 217-555-xxxx if there are any further questions.
Sincerely,

Question

I wrote a adjustment letter to practice in English. Please tell me if there are any grammatical errors.
Dear Mr. Yamada:
I was very sorry to read your letter telling me that we failed to supply computers that you ordered. We will do my best not to repeat such a thing ever again.
To resolve that, I have already got in touch with the president in your company. Your president asked to replace them with new computers to your office with no costs. Therefore, we will provide the new computers as soon as possible.
We realize that your employees have an inconvenience situation during the working hours because of our computer failures. To make up for our underperformance, let us give you a 15 percent discount coupon for your next orders.
You have been a good customer since we started an office supply business. We would not like to spoil with our relationship with you because of our computer defects that we had this time. 
Please contact me at Yamada@gmail.com or 217-555-xxxx if there are any further questions.
Sincerely,

Utente eliminato · Accepted Answer

This is more natural:

Dear Mr. Yamada

I was very sorry to read your letter saying that we failed to supply the computers that you ordered. We will do our best to make sure that this never happens again. 
To resolve this, I have already gotten in touch with the president of your company. He has requested to replace your computers with brand new ones at no cost. With that said, we will provide new computers as soon as possible.
We realize that we have caused a great inconvenience to your employees because of this mistake. To make up for this, please let us give you a 15% discount coupon for your future orders. You have been a good costumer since our business started. We would not like to spoil our relationship with you because of our mistake. 
Please contact me at yamada@gmail.com or 217-555-xxx if you have any further questions or concerns. 
Sincerely,