Railwire — Not Refunding my Security deposit

I registered for railwire broadband service on August 2020. They took[protected] refundable + 1000 installation). He didn't have me any slip and never told me it would be important at the time of refund. Now I discontinued the service after bad internet experience. But they are saying they can't provide me my security deposit back. My local provider have copy of slip in his records but not helping in this. 2500 is not a small amount. Please help me in this matter.