I was about to attach proof of communication with the company that is not responding to my reference letter request. Should I attach proof with a letter of explanation or with other company's employment documents?
You should include a letter of explanation where you mention that the company is not responding or is not ready to provide an experience letter in the requested format. Including all communication as proof in your letter of explanation. Additionally, mention that since the company did not provide the required letter, you are including additional documents to prove your work experience. You can list documents in the letter of explanation but these additional documents should be attached in the employment document section.
Additional documents you can include:
Reference letter from your friends/colleagues/manager who were employed during the same time period.
This letter is important to provide your job duties match the NOC code you have selected
Also, make sure to include any kind of proof of your friends/colleagues/managers employment with the company
Get those letters notarized (if possible) if they are not on the company letterhead
Original offer letter, and resignation / relieving letter (if applicable)
Any confirmation letter, promotion letter, or annual hike letter during the employment
Payslips during the employment
Tax Documents issued by the company e.g. Form 16 in India, W-2 in the U.S., or T4 in Canada