I think the reason for the real reciept is to check for forgery, I have had a number of companies asking for that for returning work equipment and there is no way I will send the companies documents all over so we normally come to an arrangement by using a fax, maybe you could ask them that?
To be honest I am not suprised they are not giving out email addresses to you but an addressed letter marked, Private will land on his desk. The problem without giving out email addresses is the potential for it to go into the wild, like the classic bill.gates@microsoft.com which people decided must be his real address (its obviously not), and be used nefariously.
4 people in Warranty is a bit silly though, that should be changed especially since DS is not their only UK active product now.
Sad to hear you are having such a bad time and I can't blame you for wanting to sell, but mine's been working fine *touches wood* so far.