As an ex-postie (worst three years of my life!) I know that the internal process they mention is incorrect and varies from location to location. The only sure way to get problems resolved is by writing to the 'Delivery Office Manager' for your area.
Also, the 'customer' is the sender and you, in most cases, are the 'recipient'. Don't think for a minute they care about the dozen stamps you buy before Christmas - the real money-spinners are the PPI customers and the D2D contracts.