Advice about door purchase needed

Happy_Camper_3

I need advise. I have placed an order with a company that manufactures doors and concervatories. To fix the price, I paid 10% deposit. When the final size was confirmed by my builder I needed to make slight changes before it went to their production. I have emailed them all they asked for, and I was promised that the ammended paperwork that I will have to sign (so it can go to production) will be done in 5 working days. I also made them aware that I need to place the order ASAP as it takes 4 weeks to manufacture. I was chasing them and still no results, I waited for more then 2 weeks. I could not afford to wait any longer and also got scared that if I order my door with them I will wait for it for ages. I cancelled my order because I was neglected and because of their bad services. I asked for my deposit back and was refused. Their reply was ...our T&C state that if order cancelled at this stage they will charge 10% admin fee and offered to deal with my case further and manufacture my door. I cannot trust them any more and I wonder how I can get my deposit back. As it's really not my fault that I had to cancell it. I wrote to them that I will claim it thru court but they still refuse. Please advise me what is the best way in this situation?