Advice on dealing with collections

i left an apartment complex in california at the end of 2024 and moved to WA. At the time, I explained to the leasing office I was relocating for a job and they explained what my options were: either pay the lease break fee or stay on the hook until they find a new tenant. Understanding California's "Duty to Mitigate Damages", I decided to keep paying month by month until the leasing office found a new tenant.

Flashforward about a week, they told me that they found a new tenant. We emailed back and forth and they reaffirmed I wouldn't owe anything. However, due to what they claimed were "company policies," they sent me a demand for rent based off what the lingering balance for the remainder of the full lease was and told me I was going to be sent to collections after 45 days. I explained to them it was illegal to "double dip" and get rent from both the new tenant they found and myself. They said they would correct everything when they new tenant officially moved in (they gave some excuse about wanting to make sure the new tenant they found wouldn't bail). There were some weird back and forth emails they gave me about how the new tenant pushed back their move in date, but I eventually got an updated disposition from them which showed that they actually owed me money ( because I paid for that full month and the new tenant moved into the unit in the middle of the month, so they were reimbursing me for the days in the month that the new tenant occupied the unit).

About a week after getting that updated disposition, I received a check in the mail.

I assumed everything was okay (considering the leasing office sent me a check in the mail) and that the new tenant moved in...... BUT i just got a letter in the mail from a collections agency claiming i owe this apartment complex money. That weird speech i got about the leasing office needing to send me an initial demand for rent (irregardless of the fact that a new tenant was moving in)? turns out they contacted the collections agency back then. when they sent me the updated statement that shows they actually owed me money, i would've assumed the leasing office would've dismissed the debt to the collections agency. but.... i guess that's just wishful thinking. I also found out that the collections agency has been contacting my family members as my mom mentioned she received a call.

does anyone have any general advice? i've never dealt with a collections agency before. this is a bogus debt because I already resolved everything with the apartment complex in california (they gave me a refund to account for the days I paid where the unit was occupied by the new tenant). i have no idea why they sent me to collections (when i told them back in 2024 that was illegal with a new tenant that was coming in). i.... also have no idea why they didnt dismiss the debt when they sent me the check.

I want to take my former landlord to small claims court, but.... understanding that i'd have to fly back to California.... i fear it might just be too much of a hassle. i do have all my emails saved though with the back and forth i had for the leasing office, so I know this is something I could win.