I already have a judgment against me from a debt collector, is it too late to fight it?

Not necessarily, there are still real paths depending on your circumstances. A judgment can sometimes be vacated, meaning legally undone, under a rule called CCP 473, if there was a procedural problem, like defective service, behind how it was entered. Certain income and assets can be claimed as exempt from a levy, the legal seizure of funds or property to satisfy a judgment, even after judgment. An old judgment coming up for renewal can sometimes be challenged at that stage.

This is a more limited position than answering a fresh complaint would have been, but it's genuinely worth a real conversation before writing it off as unfixable.