I have no idea whether the immigration accept will accept that letter or not.didn't you provide a notarized reference letter from your manager / colleague from that company ? I have heard many times in this forum that, in the absence of an official reference letter, this approach works provided that you submit sufficient proof of your employment.
i provided the offer-cum-appointment letter, salary slips, tax return, relieving letter, visiting card, salary appraisal letter but reference letter with job duties was missing. Still got rejection.