You want to agitate now.
Still 3Y have not lapsed after being relieved from the company.
Do you have company policies passed by the (Board of Directors)? Did you demand it in writing?
Did the company decline to supply the policy?
What is this establishment: Commercial, Industrial, Small Enterprise? It should have displayed its registration certificate near entrance?
How many people are employed in it?
What was your designation, nature of duties?
Did the company show this amount in FnF statement issued to you? Did you sign acceptance of the FnF statement?
Does it have its CSO (Certified Standing Orders? Or Does Model Standing Orders apply to it?
Are you a member of any employee’s unions, Trade Unions?
Did you sign any papers before, at the time of applying for Visa, after it?
Approach a competent and experienced lawyer/law firm dealing in such/Labor/service matters, share the above mentioned details and let your lawyer assess the merits if a case can be successfully cultivated and won built from the statement of the company “"if you want to get your relieving letter and experience letter you have to pay 3500$ which is for H1B processing fee " and also from your statement that “Note-I haven't sign on any agreement but they are showing company policies”.
Experience letter should be supplied to all employees. Refer Model Standing Orders Sec;16
Relieving letter signifies there is nothing pending at the end of employee.