scream at tech support to go fuck themselves and then destroy their equipment in retaliation
That happened in 2001 when "unlimited" cable and ADSL plans were changed to a 3GB/month cap mid-contact. And overage fees of 20c/MB from memory. With a history of metering problems this could be disastrous.
Telstra told everyone they had to suck it, until they were advised that they'd have to let anyone who wanted to leave leave without break-contract fees. But you had to return the modem. Lots of stories of people returning ash remains of the Alcatel Speed Touch Home or packing the modem with fish or banana skins. MMM lovely after a week in the post.
Eventually Telstra saw the light (flickery candle light) and allowed breaking contract while keeping modem. There were actually three get-out-of-jail-free events that year and my group of friends actually had to move so that was convenient. We used that modem with another provider until it died in a thunderstorm, but that is a story for another day.