Just read on the Slingshot forums about a user that called the helpdesk to change from Big Thing 3 to Big Thing 2.
The helpdesk failed to tell him that the plan he wanted didn't exist any more as just change him to Slingshot's better network. Causing him to have a smaller datacap and have his freeperiod hours reduced.

He asked to be change back, but they then told him, that plan no longer exists, pretty lame that they didn't tell him before that the plan he wanted to change to no longer exists. Slingshot really gutted him.

http://forums.slingshot.co.nz/viewtopic.php?f=15&t=3653