The Cashback clause on Mobile plans: How can you invoice a company which makes itself unreachable?

Since your cash back amount is given in British pounds, I shall work on the theory that you are somewhere in the Grand Old Isles... my suggestion is that you contact whatever governmental body overseeing business registrations. They should be able to provide you with a current address, and if the clerk you are talking to is VERY nice, you might get a telephone number. Good luck... and next time, listen to your better judgment. :) ...but you already knew that....