Sprint Family Plan - Strange Deal

I'm hoping that someone out there had a similar problem that I'm
having ... so any advice please?
Here is the situation:

I both a family plan with 2 year contract. After 1 year, my girlfriend
buys a new phone for 249.99 with 50 "instant" rebate which later on
turns out to be sprint rebate and they extend our contract for two
more years. Each time that I called them they were telling me that my
contract ends in March 2007, March comes around I try to cancel and
they tell me about my other line phone and the extension that I got on
the other line.

Now: I've asked them if I could cancel my account, they said that I
could but they would have to change the plan for my girlfriend which
would extend the contract for her (2 more years). Well how can they do
that if they don't have any information about her? Am I still liable
for the remainder of the contract on both lines? Is there a way to
still cancel both lines? If not, what would have happened if you break
up/divorce the other person and they move out ... what then?

BTW: That 249.99 phone was free with the new two year contract if we
knew it would have extended it we could have gotten it for free
instead.