Conversion of conservatory to orangery type thing..

Hi, I requested a firm to remove all plastic roofing and provide me with a solid roof type build with a Lantern, but keeping the same styled windows. I paid a deposit directly in their office. That was A YEAR AGO ! Since that time they have removed 2 windows (boarded them up), but they can not provide windows as originally agreed as they say steels in the roof will affect it and they have to provide new stylee windows. However, after a year, they can not provide me with windows that will look suitable to the property. They have made numerous excuses and come up with very few ideas (they have no designer !). One side was fully glazed but an element of either thick plastic or rendering will now have to be used. As far as I can see they are in breach of contract as they have not done what they said they would at the outset. It has now taken a year to get no further forward with them. I am even having to draw my own designs and I am not a designer ! Any ideas where best way to go legally as a year is a very long time ! I also presume paying my deposit and them trashing half of my original conservatory means that they accept that a contract is in place ?!