We embarked on a house extension project which included a balcony. The balcony was constructed undersized compared to the approved plans by approx. 180mm length and width.
When we discovered this and queried it with the builder, the builder declared that the dimensions could not be met because of X and Y reasons, such as plans being unclear, and also that this was verbally discussed. It wasn't discussed at all and would not have been accepted at least without a conversation with the architect. The dimensions were stated clear on the plans and the reasons given do not hold much weight in truth. The architect was informed and gave his input, basically confirming there were no constraints in meeting the dimensions. No opportunity was taken to discuss the matter at the time; the builder instead went ahead and constructed to his own modified design.
The builder is refusing to put it right or offering compensation, despite the job being costed off the plans.
I have paid X for a build and received something different without receiving any form of price reduction.
What should my next steps be?