xpd: Considering a VDSL splitter/filter is only $30 odd , charging $400 was a scam.
It is an average figure put forward by chorus.
They must drive to your house and back, time taken to correct the wiring, some houses might be a 1/2 hour job, others might be a 1/2 day job .
I guess they were trying to come up with a upfront known cost for everyone, rather than an unknown cost. Unknowns tend to scare people off.