e2save weird exchange continued...

Newway

previous story on:
http://forums.moneysavingexpert.com/showthread.html?t=342671

so I post the exchanged phone back to CPW logistics, write down the exchanged auth. no. on the package, and a cover letter explaining the situation, sent it via special delivery at my cost.
two days after that royalmail shows it was delivered. so I think that's the end of the story, but No!!!

Yesterday I received a package (via CityLink) with "Failed delivery" shown the label, and yes, it was the phone again... But apparenly my phone have been received and tampered with, because my cover letter is gone!

Now what's the best action I should take? Am I obliged to contact them? should I wait for them to contact me? and will it affect my cashback?

thanks in advance for who can gave a suggestion.