Poor carpet installation

A week and a half ago I ordered a brand new quality wall to wall carpet and installation from the Zambezi branch. I was was asked to pay the full amount upfront. The installed the carpets within 3 days but they did a very unprofessional job. The joint in the carpets is totally misaligned and their is a flaw which in my mind was caused by the installer in the middle of the joint. The joint is very visible and pulling away in places. I called the install people back on the Thursday 20th and they blamed Van Dijk carpets for the flaw and poor installation. They promised to report back on Friday or Monday this week but nothing happened. Tuesday again I went to the store to inquire and was promised feedback yesterday morning. But nothing happened they have my money now I must live with the poor installation. I will contact van Dijk today and complain about their product on Builders behalf. I do want a new carpet properly installed before I will be satisfied. For now I will not recommend Builders Zambezi as a carpet installer