When my household contents insurance bill came in recently and was more than double the previous year's figure, I was gobsmacked. However, a quick call to my insurer later and I actually ended up with a lower quote than the 2007 instalment. I'm a pretty lousy negotiator, so this felt like a major victory. There are some obvious rules if you want to challenge any kind of bill: don't rely on email (too easy to ignore); be firm but don't be abusive; assemble as much documentary evidence as possible; make sure you've allocated plenty of time so the call can be escalated if need be. But I want to know how Lifehacker readers cope when a bill with massively excessive charges (be they for broadband or the plumber) come in. Share your tips and your triumphs in the comments.