I bought mine about 3 years ago and it was a pig to put up.
You could try the Small Claims' Court but you will still need an independent report to prove the wardrobe is faulty.
In the first instance right to the Managing Director (get his name and address from head office) outlining the problems. Stress that this wardrobe is sold as flat pack for home assembly and that you had a specialist fitter do the job for you.
State that you have lost confidence in the wardrobe, you can't risk the huge door falling on top of you or a family member and as one has broken already you have cause for concern.
Stress that under the terms of the Sale of Goods Act goods must be both fit for the purpose and of satisfactory quality, and your wardrobe is neither.
Be very sure what you want before you put pen to paper. I would ask for the wardrobe to be removed, a full refund of the cost of the wardrobe and compensation for the additional expenses and inconvenience. I make that to be �380.