Landscape Breech of Contract I have a contract with landscaper to complete my…

Landscape Breech of Contract
I have a contract with landscaper to complete my new home’s yard including retaining walls, paver installation, irrigation, sod and plants. Since the walls were put up 3 weeks ago I have not heard from him. We had a different contractor come out who had done landscape work for us at a previous address and look at the wall construction. His assessment: the work is substandard. A recent rainfall put several of the walls out of level. This was the only work that was ”completed” per the contract on which I have already paid half. I am wondering what, if any, recourse I have with this contractor.