Write a letter complaining against the faulty goods.

Dear Sir/Madam,

This is to bring your kind attention that on (date), you fitted double glazing for (amount), but I have found that it is faulty. The problems are as following: firstly, the bathroom window does not close properly, and secondly, the seals on the lounge windows have failed. 

I would like to remind you that I complained about this to you three weeks back also. Although a person came out to look at the problem but nothing has been done as yet.

Considering the discomfort caused to me, I would like to claim a free repair/replacement. Kindly respond to my complaint within 5 days. 

Yours faithfully,