You have to review your contract first, when I signed my contract I also signed a presale check list. see below:
It specifically said retaining wall at buyer expense. (meaning its not in the initial quote because they wouldn't know at that time)
The other thing is you should have had an elevation survey before they dug the pool, this would have all the elevations around the pool which would also show the need for a wall.
To me it looks like it's sticking up out of the ground about 3ft. I do think you can correct some of that with dirt and grading.
I think we also need some more information from you. Are there drawings you can share where this wall will go? How high it has to be? Length of wall? materials quoted?
If it has to go around the side and back of pool 14k seems possible. Again I would get another quote, but there needs to be plans or drawings to go by to get a "similar" quote.
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