We provided a set of kitchen cabinet plans to a custom builder. The custom builder came to the house in May to remeasure and create shop / assembly drawings. July 21st we received photos of the cabinets being built in his shop. July 30th we receive an email (we were traveling) that he has to meet our GC at our home because his wall measurements showed a discrepancy with the original plans. He proposes that we extend our wall to "make it look right". We are confused and ask that it wait until our return. We come home to learn that the original plans had an incorrect wall length. Despite his remeasuring, the cabinet maker did not raise a flag/concern but went ahead and built wall cabinet to the original length. Now that the already built cabinet needs to be modified and the cabinet builder insists that we pay all costs. How should we proceed? Thank you.