This is not really an ADA issue (Americans With Disabilities Act) as it is an issue of labor laws and Family Medical Leave Act. If you are on long term disability, at some point, based on state's certain laws and case laws, a company can terminate you especially if you have been on unpaid disability since 2010. Most companies only have to hold your spot for 3 months, so it appears if the dates are correct they may have jumped the gun by a few days. Consider speaking to private counsel, the Equal Employment Opportunity Commission and your state's labor departmen about this action and see if you can get your job back or monetary compensation for the possible failure of the company to wait out the 3 months (usually 90 days).