Complete The Customization of a Zen Cart/OS Commerce mix website

Complete customization of a current website. The work is almost complete, we believe, but we have lost the confidence with the firm that has done the work so far, there are a few issues, but we have not been able to contact them, and this has been dragging for months. Our site is a zen cart based site, with some sections done in OS commerce as well as some custom programming. We have an an almost finished dev-site version of our current site. We need someone to go over what was done, complete some unfinished work that has to do with shipping quotes to customers, some page layouts for the one page checkout and the shopping cart, and fix any bugs that might appear once the new version of our site goes live.