I think you have a LOOONG road ahead of you before you can swim.
You would need to know the manufacturer, figure out if the wall was for a round or oval pool, buy all the other structural parts to suit, then deal with the busted wall seam - which may force you to buy a smaller pool size because your wall is now shorter, then make it all fit with your new CUSTOM CUT wall - I really think you should just let your neighbour "keep" the wall so you don't have to deal with it, it'll end up costing you as much as a new pool anyways without as nice an end result.
Just my 2c