Someone dropped the ball. Let's follow a window job on a journey through a typical large window and door contractor. It goes something like this:
Salesperson negotiates with homeowner and writes contract.
Salesperson leaves contract on sales manager's desk.
Sales manager checks that price is acceptable
Sales manager passes contract on to recheck person who measures windows.
Recheck person passes contract and measurements to ordering person who then orders all of the materials according to the contract and the measurements.
Contract is passed to installation manager. When materials are ready the installation manager hands the contract to which ever installation crew is available.
Installer contacts homeowner to arrange installation date.
Installation crew installs products and asks for payment of balance.
If it seems like there are a lot of opportunities for mistakes and miscommunications in that process, that's because there is and they do happen. Deal with a company with a better approach.