Is it possible for you to get an email from your employer that they cannot provide the letter?
If your employer is not providing any letter or email, you can write a letter to CIC mentioning your situation and attach all other necessary documents such as Relieving letter, Experience letter, last 3 months payslips.
In case they did not accept your experience and if you have 4+ years exp, then it should not be much of a problem since you will still be 3+ yrs exp even without this exp. Just calculate your points according to your exp. Let me know if you have any doubts.