Hi,
you need to ask for proof of posting, they do not give them out otherwise.
Pick up a lost post form from the post office and fill it in. when you read it, you will probably decide to not bother and throw it in the bin. It is so complicated and ask's so many questions that I ( run an internet bussiness) don't bother. if it's missing, then thats it, but, I have had packages returned to me weeks after I posted them, but if there is no return address, then it will probably be lost forever. The post office want you to fill the form in so they can see if there are any dodgy postman who are stealing stuff, they don't want to refund your money.