I got that letter I think last year. When I called them they tried to hide under "we want to find out how to improve products so you don't have to return things & to improve my return rate". If that was the case then why not just send a questionaire or get a call centre person to contact me, not accounts. Sometimes I can place orders and not send anything back for say 8 months or something, then I'll all of a sudden send a few bits back at once. They just look at percentages over time and not the pattern of keepers/returns.
When I mentioned what people thought about the letter on this forum they got quite defensive and would only talk about my account. They couldn't understand that I was trying to give them an overview of what their customers were saying as I had the opportunity to give feedback.
They also wanted me to think about my orders before placing them. Now I don't order a great deal of things. I keep a fair few items but also return a fair few like when I think a Beth Terrell jacket looks great on little Pipa but when I get the XS home it swamps me. I told them that most returns would have been due to sizing on clothes/jewellery and that is something they can't do much about when the ring size should fit or the top measurement is correct in theory but then doesn't fit. Some purchases just don't work out. You can always tell them that under the distance selling laws you are within your rights to return any purchase. Whether a company gives 7, 10 or 30 days makes no difference it's your right to return.