Renege on agreement

Just 5 Weeks after marbeliting my pool a hole appeared in the new marbelite. It was agreed by the Principal of Acme Pool & Spa who did the marbelite, that the problem would be rectified to my satisfaction and that after the repair the hole and surrounds would not be noticeable. However subsequent to the repair a large stain now is seen where the hole existed. Obviously this is unsightly and spoils the pool. This is in contradiction to our agreement, and now the Principal has reneged. I have copies of correspondence confirming our agreement if sight is required