I need to be clear about what I am legally entitled to claim from the company, and what they may agree to on commercial grounds (for goodwill reasons).
Are you saying that, legally, the limit of my redress is only the cost of having someone else finish the work? What about all of the time that I have had to take off work whilst they have tried and failed to complete the installation? This amounts to about £1,500.
Also, no doubt Everest would say that all product warranties (lifetime guarantees etc) would be void if they do not complete the installation.
Am I not entitled, under some form of consumer legislation, to set out my dissatisfaction with their product / service (which has been terrible) and thereby avoid the original agreement? They have repeatedly failed to deliver the product / service I purchased, and I have no confidence in their ability to perform as per our agreement.
As it is not a practical solution for them to put my old windows back as they were, I would propose that they accept the deposit I paid and subsequent monthly instalments (amounting to about £2,000) as full and final settlement?