We contract company X to fit a conservatory. As part of the process we choose a specfic type of glass to be fitted to the roof. In the contract it clearly states the type of glass. When the conservatory is fitted we are doubtful on this glass and think it is wrong type. The glass came with a delivery note stating the type/model number of the glass so we took this off the packaging before they threw it away. We then contacted the supplier of the glass (3rd party) and they confirmed the order had been made for the a different type of glass to the one we had originally ordered. This 3rd party supplier does not even sell the glass we ordered. I then contacted the supplier who should have been used to supply the glass we were sold. They told us that all their glass had a specific mark on the windows. Ours do not have the mark. I am therefore confident they have supplied us with a cheaper version of the glass we have ordered. It is a similar type of glass from a different supplier. A case of 'ordering heniz beans and getting lidl's'. Now, obviously we are not happy about this, but are wondering about the best way to go about dealing with the situation. I believe, even if we are satisfied with the work, we have 28 days to pay from the point they invoice us? The outcome we would like is that they remove the cheap glass and provide us with what we have ordered. How shall we phrase this to them? thanks!