i had the exact same issue
i had a tytn on the orange world unlimited, and i upgraded to the tytn2 back in october and was told that all bundles etc will roll over for the length of the new contract

i was on orange premier 600 too, which meant i could upgrade after 9months, and it was a 12 month contract.

i got a bill in feb08 for £230 which is about 4x my usual, so i moaned to Orange.
they told me i was wrong a few times, and that i should have known that the orange world unlimited was due to expire. which i wasnt told.

so the only way they can offer me a decent data allocation is to put me on panther 75 web or something, which is 250mb per month
but its an 18month contract

so i had to lose my lovely "upgrade every 9 months" tarrif and now im stuck with 18month!

to make matters worse, they still havent refunded me my data costs for that month (~£150) despite assuring me that it'd be done on my next bill date. i've been waiting for 4 months now...

i really really really hate orange now... after being with them for 9 years they just screwed me over too many times

i think if you get a nice looking sales girl with a big chest then you should count yourself lucky, my lad...