You will have to go back to your contract

How much does the contract allow for liquidated damage as a result of such delay? If there is no such clause, then it's a matter of whether such a significant delay is counted as a material breach of contract by the contractor. The deciding factor is still in the contract.

Of course, the above only matters if you decide to go to the court. Otherwise, try to be nice with them and ask for the balance back from them.