It is good to know that your sponsor gave you all your dues. Many companies use the loopholes in the system to snatch away the ESB of their employees. However, it sounds strange that while your company has paid your dues in full, it is refusing to give you to cancel your visa. I would suggest you try to handle the matter in a diplomatic way with your HR people. If that doesn't work, go over to the National Human Rights Committee and lodge a petition. They will handle the matter and help you out.