If customers take the time to write in with observations, comments, critique, it is rude for communications not to be acknowledged. Yes we all receive phone calls from large organizations, but this is probably to ensure there is no written record of a response of the incident.
I accept large companies receive large volumes of mail, this is not an excuse for rudeness. If the person the letter is addressed to cant reply, then somebody else ought to.
I have just had a very similar experience with T Mobile. The recovery in terms of T Mobile finding a solution, involved 3 contracts being halved and 2 iPhones 5’s being given gratis.
This was obviously a serious issue, but my initial letter remains unanswered. This is just plain rude!!