ISPs have no shame. There's hope of getting anywhere with that.
Most have fine-print in their contracts that unlimited isn't really unlimited.
One thing you can do is look into a business account. You pay more, but you get unlimited bandwidth, and can often run servers and such that aren't allow with a consumer account.
If you want to try to fight the issue, look carefully at your bill and what taxes are being applied. Look up the text of the laws the taxes are based upon. If memory serves one of the common taxes that has to do with telecommunications (wish I could remember the name) has certain requirements of not interfering with you usage in certain ways that /should/ keep them from capping you.