You cannot go to a company where you got an offer Write a letter to the HR supervisor to explain the reason why you decline the offer express you gratitude explain you like your current job very much

Dear Sir,
My name is Duy Anh. I was one of the interviewees who was selected for the opening positions in the marketing department. However, I am writing this letter to inform you that I must respectfully refuse your offer. I was promoted to team manager last week at my current company and after consideration, I came to the conclusion that I should stay. This promotion will offer me more opportunities although the salary does not increase.
I would like to thank you and the HR department for setting up an interview and giving me the job opportunity. I had a wonderful discussion with the CEO and he personally took me on a tour throughout the office. I was very impressed by his hospitality.
Although the offered salary is very attractive, the job is not challenging enough for me and there is little room for improvement. With the promotion at my current company, I take on more responsibilities but also more lessons to be learned.
Thank you for your consideration and I apologise for any inconvenience that I might have caused.
Yours faithfully.
DA