IIRC (I might be wrong on this) for a lien to be valid they have to send you a copy certified mail. If you have not gotten that, nor see anything on the county recorder’s website (link above), you do NOT have a lien against you.
(I assume you’re in San Diego county- I know you were in San Marcos or Oceanside before)
The angry guy on the phone might be bluffing entirely.
And if has a license (check cslb.ca.gov… not sure if pool maintenance requires a license…) report all of this to the state contractors board (cslb).
BUt if you’ve never received a 20 day notice aka preliminary notice, he can NOT file a lien and have it stand. And even if he files it now – it would only look back 20 days… So you wouldn’t owe multiple months.
(In our contractor nightmare we had a supplier who hadn’t been paid by the general serve us a 20 day notice more than 60 days after the contractor walked off the job. We called and explained that the job site had been closed for 60 days – and we had the CSLB complaints and bond claim records to prove it. No 20 day lookback applied since it was more than 60 days. They never filed a lien.)