That's because you don't, they just sent the letters out by mistake.
The next letter you need to send is to ask why people who bought a 2 year season ticket last year haven't been offered a discount on the 2010-2011 season, but people who bought a 2 year season ticket this year have.
In the past, I've been the first to seize the opportunity to have a bit of a rant about the club shop, however the customer service in there has improved immeasurably IMHO in the past year or so.
Seems like there's still work to be done ...