SSDA refuses to pay refund

The company is refusing to pay my refund under the excuse that they are still conducting an investigation. It has been over six weeks since I sent them my documents for a refund. They know that the money does not belong to them but still they are keeping it for themselves. However they are so quick to harass people for whatever debt they owe. This is not a company you should trust at all. The 14700 that I accidentally deposited into their account is like millions to them now. They don't want to release it and they are now giving me excuse after excuse. I. am so tired of waiting for what is rightfully mine. I am going to sue the pants off this company