Can I sue a debt collector even if I actually owe the debt?

This trips people up more than almost anything else in this area. Owing money and being collected from unlawfully are two completely separate questions, and a lot of people assume that owing the debt automatically forfeits any complaint about how it was collected.

It doesn't. Two laws cover this, the federal FDCPA and California's own version of it, the Rosenthal Act, and both regulate conduct, not debt validity, harassment, false statements, contacting people who have no business being contacted. None of that becomes acceptable just because the underlying balance is real. So the honest framing is: your debt situation and your treatment during collection get evaluated on entirely different tracks.