Royal Mail now have a system of pricing in which large envelopes (a category which includes A4 size) require a special stamp costing 44p to post.
Actually this is not a very new system any more and it was widely reported and publicised at the time of the change, way back in 2006.
If you post an A4 envelope containing your headshot and CV to me with an ordinary first class stamp on it you will save yourself 12p. Ooh yes, a whole 12p, you crafty thing. You will, however, cost me Â£1.16 to retrieve your envelope (which I will do, in the vain hope that it is a large sponsorship cheque from a business).
I particularly resent this happening now that auditions for the show in question have already been held.
If you have not had any work recently, could I suggest you start a) using the correct stamp and b) sending your CV to people within, say, a month of the audition notice being put up.