I'm not sure anyone can help you with this, except an attorney. Without seeing your contract, I have no idea what you agreed to, and even if I saw the contract and total billing, I wouldn't know what's normal in your area.
I can tell you prices for concrete pools tend to me much higher in rural areas, compared to urban areas. Prices are very low in Florida, and tend to get higher as you move inland, northward, and westward.
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