There's a lot going on in your question, and not all of it makes sense. First of all, you probably aren't receiving SSI, but SSDI. SSI stands for Supplemental Security Income, and is Social Security's disability program for poor people who haven't paid enough into the system to be entitled to a benefit based on their earnings. SSDI stands for Social Security Disability Insurance, and is what people get when they have paid FICA taxes for at least five out of the last ten years. If you worked, and paid taxes, for the past 11 years or more, you are almost certainly receiving SSDI and not SSI. Also, if you were receiving STD and LTD payments, you probably weren't poor enough to qualify for SSI in the first place.
I'm not surprised that they're asking you to repay the STD and LTD benefits because of the SSDI benefits. Most STD and LTD plans have a provision that says they offset SSDI benefits, and if they pay for a while before you receive SSDI, and then you receive a big award of SSDI "back pay," the LTD carrier will usually want to be repaid, and most policies say they should be. In most cases, if the policy says they can ask to be repaid, there's not much you can do about it. There are a few policies that don't say that, though, and a few policies that don't say it correctly, so if you want to try to get out of it, you should talk to an attorney who handles employee benefits issues.
Finally, you mentioned something about your employment status changing - I'm not sure what you mean by that. In most cases, once someone has exhausted FMLA and other forms of medical leave, it is perfectly legal for their employer to officially terminate them if they are no longer able to perform their jobs. However, this doesn't mean that your LTD benefits should end.
Jeremy Bordelon is a licensed attorney in the State of Tennessee only, and is authorized to practice in all Tennessee State and Federal courts, and before the Social Security Administration in any jurisdiction. Please call our firm at 1-866-959-5362 if you would like to discuss your case in more detail. The answers provided on Avvo.com are for information purposes only, and should not be relied on as legal advice. This answer does not create an attorney-client relationship between us. In some jurisdictions, this answer may be construed as attorney advertising.