Same thing here: "... Unfortunately we are unable to verify your details on our invitation list... blah blah blah. If you did receive an invitation from us, and you believe this to be an error, then please contact us ... blah blah blah"
My reply:
As you were "unable to verify my details on your invitation list", I have enclosed (attached) a copy of my invitation. I'm sure this will clear up matters and you will adjust my balance accordingly.... blah blah blah
Thank you...
(My invitation? Click the attachment)
P.S I haven't heard back from them yet but I suspect they buried my invite even deeper in the outbox