Please take a look of that site to help organise your cashback and check when everything needs to be sent back.
"The cashback calculator tells you when your claim window starts & ends for each section of your offer.
We do not restrict you to a single specific bill and you need to send the most recent bill for the claim window specified (Please note the bill should not be older than 28 days when you send it in!)
To view your claim dates and use the cashback calculator you will need your order ID and mobile number or email address.
-Click on the logo for the company you purchased the phone from
-Enter your order ID
-Enter either your mobile number or email address
-You can now view your order and details on when you claim your cashback
If you do not know your order ID you can use your mobile number or email to have this resent to you via the log in page of the cashback calculator."