Your posting indicates that you have been "terminated" by your company for some misconduct, which is better known to you. If an experience letter is being issued, it may not be helpful to you in any manner, as your employer will definitely mention "termination" as the reason for leaving. In my suggestion, it would be better if you can manage without that experience letter; in its absence, you can use the salary slip and appointment letter. Your employer asking for money is nothing but a way to show denial for issuing an experience certificate.