Boohoo.com poor customer service regarding refund

Ordered 3 dresses on 11/3/2012 for Saturday delivery.
Items delivered by mini cab driver on Saturday 17/3/2012.
Items not suitable (poor quality/sizes) therefore returned to Boohoo by Royal Mail Special Delivery.
I have tracked the parcel which was delivered and signed for by Boohoo on 21/3/2012, however they are claiming non receipt of the items.
I have provided the tracking no. , RMA NO. , Order no., item code nos.
Sent 8 emails to their Customer Services team to no avail
Their customer service is really poor I am disgusted with them.

All the information I have provided shoud be sufficient for them to go on Royal Mail's website and see that the parcel was delivered and signed for. If the parcel has been lost or mislaid by their warehouse that is an internal problem for them to sort out within the company. It is ridiculous that they will not refund me.
They are now saying that I have to post my original postal receipt to them for them to investigate
(photocopies not acceptable)
Whose to say that they will also claim non receipt of the original receipt !!!