More information is needed to fully answer your question. For example, were the carts that struck your car left in the parking lot by other customers? Also, "acts of god" such as sudden storm may relieve the grocery store from liability. Given that the store has denied liability, I would recommend that you contact an attorney to discuss your options.
This response is for informational purposes only and is not, nor is it intended to be legal advice. No attorney-client relationship is created by this answer. An attorney-client relationship may only be created by written agreement of the parties. This information is not a substitute for seeking legal counsel from an attorney with whom you have an atttorney client relationship along with all the privileges that relationship provides.
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