If you have an attorney, you should consult with him/her. If not, you need to retain a personal injury attorney. Slip and fall cases are not always straightforward and often require an expert to evaluate the surfaces where the incident happend. best of luck.
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It sounds like you have a lawyer. Consult that lawyer to move forward with your case. Typically, if an insurer does not respond to a demand letter in an acceptable way, your option is to file a lawsuit. You should talk with your lawyer about this. If your lawyer is no longer interested in pursuing your claim, you should consult with another local lawyer who can help you. Good luck.