Can anyone help with these two queries

1 I have moved address recently. I have changed my address with Amazon in at least 3 different places. They seem to know my new address but "Return to" address printed on the postage label still shows my old address.

2 The note at the bottom of the label "Post by the end of (date) " -- is this something that Amazon want you to do or is it something that Royal Mail want you to do(ie if you post after the date the label is no longer valid)

Thanks