Ya, there's also Ripoff report. While BBB isn't really anything enforceable, I've seen such a threat work. For example, my friend brought a car into Midas for something and then he got charged extra for work that was not approved (only like $35) and I over heard the dealer say, "But it was black you needed it changed." My friend was like,"but I didn't say to do it...I don't want to report you to the Better Buisness Bureau..." and the mechanic let it go.
Does the dealer have proof that it's expired? Just ask for a print out of the service contract from them.
Could the individual you bought it from be lying? If not, I would do a small claims court because someone has to stand up to those dealers.
The finance manager is just a middle person maybe. Talk to someone higher.